WHY, AND TO WHAT EXTENT, IS SEXUAL INFIDELITY WRONG?

: Sexual infidelity is widespread, but it is also widely condemned, yet relatively little philosophical work has been done on what makes it wrong and how wrong it is. In this paper, I argue that sexual infidelity is wrong if it involves breaking a commitment to be sexually exclusive, which has special significance in the relationship. However, it is not necessarily worse than other kinds of infidelity, and the context in which it takes place ought to be considered. I finish the paper by looking at how the hegemonic norm of monogamy makes infidelity both more likely and more difficult to deal with.


Introduction
Sarah and Chloe have been together for 3 years and live together. They are in love and are in a monogamous relationship but not married and without children. They are happy together and have an equal partnership, sharing domestic and emotional labour equally and so forth. They both have similar income levels and are at a similar level of seniority at work. Sarah is away at a conference in Rome and has a few glasses of wine at dinner. In the hotel bar that evening, she meets Julia, and they end up having sex. Sarah knows that she will never see Julia again, because she lives in Italy, and they do not exchange contact details or even each other's surnames. Sarah tells no one about the encounter and returns to Chloe and gets on with their relationship as if nothing has happened. Sarah's feelings for her are unchanged, she never cheats again and Chloe never finds out.
Why Sarah has committed wrong here, and how wrong that is, will be the focus of the paper. In most Western democracies, sexual infidelity is now a monogamous relationship with someone else. 2 Sexual infidelity can also take place in non-monogamous relationships. For example, three people might be in a polyamorous relationship but agree to be sexually exclusive to just the three of them and one sleeps with someone else, or two people might be in an open relationship but promise not to have sex with any mutual friends and one breaks this promise. Most of my discussion, for simplicity, but also because, statistically, most romantic relationships are at least purportedly monogamous, will focus on the monogamous case. However, it is important to remember that this is not the only form that sexual infidelity can take.
Of course, 'sexual activity' is a contested term, and to provide a full definition of it is beyond the scope of this paper. Therefore, instead, I will rely on our common grasp of the term, with examples being vaginal and anal sexual intercourse, oral sex, mutual masturbation, BDSM and potentially phone sex and 'sexting'. 3 By 'monogamous relationship', I mean a two-person romantic relationship in which the partners have agreed, implicitly or explicitly, to love only each other romantically, and to have sex with no one outside of the relationship. I am conceiving of a romantic relationship as a relationship that is similar in kind to a marital relationship, although I do not want to limit my discussion to marriage. 4 It might be worse to commit sexual infidelity if you are married, but as it seems obvious that one can be sexually unfaithful when not married, the wrongness of sexual infidelity cannot depend on the marriage contract. It is partly for this reason that I am using 'sexual infidelity' instead of 'adultery', which has connotations of extramarital sex, but also because 'adultery' is often interpreted more broadly than just sexual infidelity.
Further, sexual infidelity can, and often does, have aggravating factors, which make it a far more serious breach of obligations to one's intimate partner and deepen the betrayal. One of these aggravating factors might be that the partners are married, as marriage, for some people at least, entrenches the obligations you have towards your spouse, and might also include religious reasons to not commit adultery. Other 'aggravating factors' could involve the unfaithful partner failing to fulfil other obligations to the relationship, for example, the unfaithful partner using shared finances to pay for hotel rooms to sleep with his or her lover or the unfaithful partner engaging in a protracted period of deception, perhaps involving third parties. My discussion will focus on the act of sexual infidelity itself, not on the aggravating factors. This is because the purpose of this paper is to isolate what could be distinctly wrong with sexual infidelity itself, and how bad that wrong is, even in the absence of other wrongs.
In addition, sexual infidelity often takes place in relationships with unequal power structures; indeed, perhaps most romantic relationships are unequal in some way. Sexual infidelity is much more problematic when the relationship is unequal, and the partner with the most power is unfaithful, particularly if the inequality means that the other partner would have great difficulty exiting the relationship. It is also much more problematic if one partner has greater opportunity to commit sexual infidelity than the other, for example, if one partner is at home looking after the children, while the other is often working away. As I take unequal power structures in romantic relationships to be a serious issue, and abuse of one's power in an intimate relationship to be a serious wrong (although a full discussion of what this means and why it is would require a paper of its own), for clarity, in this paper, I will assume that the romantic relationship in question is an equal one. I understand that this might mean that a lot of my discussion will jar with some people, who find it unhelpful to discuss ideal relationships rather than actual ones. 5 However, as the purpose of the paper is to look at the wrong of sexual infidelity in itself, I need to assume that there are no other issues accompanying it. This is why I am using the Sarah in Rome case as the 'prime case'. The rest of the discussion will focus on this kind of case, although I will consider other examples as well.

THE PREVALENCE OF SEXUAL INFIDELITY
Sexual infidelity has almost certainly occurred for as long as monogamous institutions have been in place, and it continues to occur, probably in all cultures, even when it has been illegal and punishable by death. It is difficult to know with any certainty what percentage of people commit sexual infidelity, but studies suggest it is relatively high in the UK and USA, at least. Some example statistics are as follows: a Gallup poll in 2008 found that 54% of Americans knew someone with an adulterous spouse (Jones 2008). Judith Mackay, a senior advisor for the World Health Organization, found in 2000 that 50% of Americans and 42% of British people aged between 16 and 45 had been sexually unfaithful (Mackay 2000). A study in 2006 found that 70% of American dating couples reported at least one incidence of infidelity in their relationship (Allen and Baucom 2006). In addition, research suggests that men and women now engage in infidelity at similar rates (Fincham and May 2017). This is perhaps because of women now having greater opportunity to be unfaithful than previously.
Of course, it would be a mistake to think that its prevalence justifies it. Lying is undoubtedly more common than sexual infidelity, but that does not give us reason to abandon truth telling as an ideal or to fail to condemn lying. However, the commonness of sexual infidelity does tell us that monogamy, while seeming to be a widely held ideal (as we saw above, 90% of Americans disapprove of adultery), is something either we are very bad at or that it is not actually held in as high regard as it might seem. Either way, its commonness calls for greater clarity over why sexual infidelity is wrong and how serious a wrong it is. PACIFIC PHILOSOPHICAL QUARTERLY

Why might sexual infidelity be wrong?
3.1. HURT A striking feature of sexual infidelity is the degree to which it hurts and the degree to which people, including those who have never experienced sexual infidelity, seem to understand the hurt and see it as reasonable. Indeed, up until 2010, the defence of provocation could be used in the UK if someone killed their spouse because of their sexual infidelity. Of course, sexual infidelity has such extreme consequences only rarely, but it is not uncommon for it to lead to divorce or the dissolution of a relationship when the sexual infidelity is found out. A summary of research into infidelity from 2017 found infidelity to be the top cause of divorce in the USA (Fincham and May 2017). The 2008 Gallup poll mentioned above found that 62% of Americans would leave their partner for being unfaithful, and 64% would never forgive them (Jones 2008). Ending a relationship, of course, can be a huge upheaval. There might be children involved, shared property, shared finances, shared friends, and a shared life together, so for sexual infidelity to cause the end of the relationship, especially if it was otherwise good, shows how significant it is taken to be. When it does not lead to the end of a relationship, it still frequently has detrimental effects. A survey of marital therapists in the USA carried out in 1997 reported that, second to physical abuse, extramarital affairs were the most damaging problem to relationships (Whisman et al. 1997).
Therefore, sexual infidelity causes hurt and thus might be said to be wrong because by committing it, the unfaithful partner hurts someone, and this person is someone to whom they have significant obligations and whom them purportedly love. As Bonnie Steinbock puts it: 'to cheat on one's spouse indicates a lack of concern, a willingness to cause pain, and so a lack of love' (Steinbock 1986, p. 13).
However, there are two related problems with this explanation of its wrongness: (i) If wrong, sexual infidelity is wrong even if it does not cause pain; (ii) if their hurt is reasonable, they are hurt because they are wronged, not wronged because they are hurt.

If wrong, sexual infidelity is wrong even if it does not cause pain
If wrong, sexual infidelity seems wrong even if the person cheated on never finds out and so is not hurt. If not, then unfaithful partners who never get caught would not have done anything wrong, and it would seem strange to have done something wrong only if you are not good enough at deceiving your partner. Sexual infidelity might also be said to be wrong even if the person cheated on finds out, but is not hurt, perhaps because they have also WHY, AND TO WHAT EXTENT, IS SEXUAL INFIDELITY WRONG? been cheating, or because they simply do not mind. It might be objected that it is wrong because there is always a possibility of the person being cheating on finding out and being hurt, but this seems to get things the wrong way around, implying that if you can ensure that they will not find out, then the infidelity is unproblematic. Here, I draw on David Archard's work on the wrongfulness of rape, whereby he argues that the hurt caused by rape is evidence of its wrongfulness, but not constitutive of its wrongfulness, as we can conceive of a 'hurtless rape', such as when a woman is drugged and raped but does not remember the rape and never finds out about it (Archard 2007, pp. 379-380). In such a case, the woman is still wronged, although not hurt, just as the romantic partner could be wronged by a 'hurtless infidelity', where they are cheated on but never find out. Similarly, if sexual infidelity is wrong, then the hurt it causes will be evidence of its wrong but not constitutive of it.
3.1.2. If their hurt is reasonable, they are hurt because they are wronged, not wronged because they are hurt This leads to the second issue: It seems odd to say that the person who is hurt by sexual infidelity is wronged because they are hurt; rather, if their hurt is reasonable, then they are hurt because they have been wronged. I said above that sexual infidelity often causes the dissolution of a relationship, but this is usually because it is considered a grave wrong. To hurt someone, even someone you love, is not always morally wrong. For example, it might not be wrong if what you have to do in order to not hurt them places an unreasonable burden on you, if you were not able to do what was required to avoid the hurt, or if you were not aware of what was required, and could not have reasonably be expected to have known or find out. Sometimes, the person hurt is wrong to be hurt. A very possessive boyfriend who does not want his girlfriend to talk to any other men might be hurt when he sees her talking to a male work colleague. However, what he needs her to do in order to avoid hurting him is unreasonable so should not count as a reason for her not to talk to other men. Similarly, a person who has freely consented to be in an open relationship with their partner might be hurt when their partner has sex with someone else, but this hurt, while understandable, is not in itself a reason to accuse their partner of having done something wrong. Therefore, if the hurt caused by sexual infidelity is part of the reason for its wrongness in a given instance, the hurt must be justified, and this justification will need to be something other than the hurt itself.
A further problem with the idea that sexual infidelity is wrong because it causes hurt is that there are morally dubious reasons for which one might be hurt by sexual infidelity, which we might not want to pander to. One might question the wrongness of sexual infidelity by looking to the history PACIFIC PHILOSOPHICAL QUARTERLY of marriage and monogamy as a way of controlling women's sexuality, in order for men to ensure that their children really were their children, but also, perhaps, because monogamous marriage is a way of gaining property rights over one's spouse. John McMurtry advances this kind of critique of monogamy, arguing that monogamous marriage serves the capitalist order in various ways, including preserving the principle that some people can 'legally acquire the use of other people's personal powers from which they may exclude other members of society' as 'husband and wives contractually acquire for their exclusive use their partner's sexual properties' (McMurtry 1972, p. 597). On this reading, sexual infidelity would be wrong because it denies a person their right to exclusive use of their property, and the person who has been cheated on is justified in being hurt because of this denial. However, this is a bad reason to be hurt and so the hurt might not count as a reason to be sexually faithful.
In addition to morally dubious reasons to be hurt by sexual infidelity, people who have been cheated on are often hurt because they see the sexual infidelity to have certain meanings or implications that the unfaithful partner may not see it as having. People who have been cheated on often see it as a great betrayal, a humiliation, an indication of a lack or loss of love, a sign that the relationship is over and that they are not 'enough' for their partner, and so on. The cheater, on the other hand, may see it as 'just a drunken mistake,' which 'meant nothing'. I will discuss the disjunct between the way that the unfaithful partner and the partner who has been cheated might see the significance of sexual infidelity in the final section of this paper. For now, it is enough to say that this disjunct makes it harder to assess its wrongness based only on how much it hurts the person cheated on. If Chloe is hurt when Sarah has cheated on her because she believes it means that Sarah no longer loves her, when Sarah in fact does love her very much and did it because she was drunk and wanted to feel young and desired again, then there is a sense in which we can say Chloe's hurt is misplaced.
Thus, although hurt is, of course, part of the story, sexual infidelity, if wrong, is wrong not only because of the hurt caused by it. The hurt is evidence of the wrong of sexual infidelity but requires further elucidation to explain why it is justified.

DECEPTION
I cannot give a full account of the wrong of deception here. There are many types of deception, and it is contentious whether all deception is wrong. For the purposes of this paper, it will suffice to say that deception is wrong if it shows a lack of respect for the deceived person and/or if it makes their life go worse for them that it would have gone were it not for the deception. If sexual infidelity involves deception, which it often does, then the deception will be a wrong-making feature of it. As Richard Wasserstrom puts it, 'lies, WHY, AND TO WHAT EXTENT, IS SEXUAL INFIDELITY WRONG? half-truths, clandestine meetings, and the like may become a central feature of the adulterous spouse's existence. These are things that can and do happen, and when they do they make the case against adultery an easy one ' (1998, p. 142).
Deceiving one's partner about one's infidelity might be considered to be a kind of manipulation, 6 a way of getting one's partner to act in certain ways through false beliefs. By deceiving one's partner into believing that they are in a sexually exclusive relationship, the unfaithful partner manipulates their partner into continuing to act as if they are in a sexually exclusive relationship, when in fact they are not. It may seem too strong to suggest that Sarah in our example is deliberately manipulating Chloe. Nonetheless, any sexual infidelity involving deception is a form of 'free riding', hence the term 'cheating'. By committing sexual infidelity while pretending to be monogamous, the unfaithful partner gains the benefits of his partner having sex only with him (unless his partner is also secretly committing sexual infidelity) and the benefit of having sex with someone else. Even if this is not his intention, he 'free rides' on a monogamous agreement. This is not fair on the partner who is playing by the rules on the assumption that they both are; as Wasserstrom notes, it might have been hard for that partner to restrain himself, and he may have done so only on the proviso that his partner was too (Wasserstrom 1998, p. 141).
Furthermore, if deception is involved, then the unfaithful partner also deceives their partner about the significance of the sex that they have. If Sarah and Chloe are in a sexually exclusive relationship, when they consent to have sex with each other, they do so on the understanding that the sex they have is exclusive. Sex can be a different experience when it is exclusive. If, when you consent to sex, you do so with the belief that your sex is exclusive, you do not consent to non-exclusive sex, which might, for you, come along with a variety of different and unpleasant emotions, such as anxiety or insecurity. 7 In addition, for some people, the exclusivity of the sex will make it a more special experience. Hallie Liberto argues that this view of sex objectifies our romantic partners: 'When we treat our partner's sexuality as more valuable to us because access is limited, then we treat it in the same way that we treat a privately owned painting' (Liberto 2017, p. 411). There is truth in this, and often people do have problematic possessive attitudes towards their partners, which make them desire monogamy. However, for some people, exclusivity just makes their sex more intimate and important, in a similar way to how sharing secrets can feel more intimate and important the fewer people know about the secret. In any case, if, as a couple, you decide to be sexually exclusive for particular reasons, such as to express love, or to be symbolic of your togetherness, then these reasons will be part of the background to your sexual activity. Therefore, if you find out that your partner has cheated on you, and lied about it, you might feel that the sex you had together did not have the meaning you thought it did, and this could feel like a serious betrayal and/or disappointment. 8 Therefore, it is wrong to deceive your partner about your sexual infidelity. However, this raises a further question over whether it is the deception that is doing the wrong-making work rather than the sexual infidelity. Presumably, in most cases, the reason why the unfaithful partner is deceptive about their infidelity is precisely that the infidelity is deemed to be wrong, but if it is wrong even without deception, then deception would be an 'aggravating factor', rather than intrinsic to the wrong. Furthermore, of course, sexual infidelity need not involve deception: Sarah might tell Chloe as soon as she gets home about Julia. She might even tell Chloe before she sleeps with Julia that she plans to do so, and she might tell Chloe that she is happy for her to sleep with someone else too, thus avoiding the charge of trying to free ride on her monogamy. If, although, Chloe did not give her permission for her to sleep with Julia, then she has still cheated on her, even though there is no deception involved and her intention is not to 'free ride' on their monogamous agreement. In addition, in some cases, sexual infidelity might seem worse when it does not involve deception. Suppose Sarah cheats on Chloe in front of her face; this could seem more callous and humiliating for Chloe than for her to do it discreetly. While this does not show that it is always worse to tell one's partner if one has cheated on them, it does show that it is not clear-cut that cheating-with-deception is always worse than cheating-withoutdeception.
In addition, as I will argue later, the dominance of the norm of monogamy makes it particularly difficult for people to be honest about their infidelities. Therefore, although it is a serious wrong to lie to someone about being unfaithful to them, we should also consider the context in which 'lies, halftruths, and clandestine meetings' take place, as people would likely be more honest about their infidelities were the norms governing relationships different. I discuss this in the final section of the paper.

COMMITMENT-BREAKING
As I have shown above, hurt and deception are not essential components of sexual infidelity, nor do they explain what constitutes its wrongness, although they might make a given instance of it worse. There are two essential parts to it: it is a kind of infidelity, a broken commitment, and it is sexual. In this section, I deal with the broken commitment; in the next, I look at why it being sexual might be significant. What unites all cases of sexual infidelity, including those cases that do not involve deception, cheating, hurt, or other aggravating factors, as well as those that do, is that they are cases of a broken commitment. 9 The 'infidelity' part of sexual infidelity depends on there being a commitment to be faithful to. Wasserstrom argues that sexual infidelity is prima facie morally wrong because it involves promise breaking (Wasserstrom 1998). However, a promise to be sexually exclusive is not often explicitly made by couples. Therefore, it makes more sense to see it as a commitment, which may be tacit, and not clearly defined but rather based on conventions associated with romantic relationships. This makes it particularly difficult to assess morally.
Nonetheless, breaking a commitment seems to be at the root of the wrong of sexual infidelity. However, the commitment is not just any old commitment. Sarah might break her commitments to Chloe all the time: She might break her commitment to spend less time at work, to do more housework, or to go with Chloe to visit her mother every Sunday. The commitment to be sexually faithful is different. It is generally held to be an extremely important commitment, such that breaking it might lead to the end of the relationship.
However, there is often confusion over what this commitment amounts to. This is at least partly because few couples actually work that out together and, instead, just readily accept the convention that their relationship will be monogamous. Of course, being sexually faithful means not having sex with anyone outside of the relationship, but does it mean not wanting to have sex with anyone else too? Are you more faithful if you never want to sleep with anyone else, or if you want to all the time but manage to control yourself? There is also the issue that this commitment will be much harder to keep for some people than for others. Some people are not interested in having sex with anyone else, perhaps they are not very interested in sex at all, or they just really like monogamy. Others get a lot of value out of having sex with a variety of new people. Some people might never have the opportunity to have sex with anyone else; others might have opportunities all the time. By way of comparisonit is much easier to promise to not drink alcohol if you do not like alcohol, or you live in a society which forbids it, than if you are part of a culture in which alcohol is an integral part, and you love drinking. It seems plausible that the differences between people's dispositions, values, and situations ought to be taken into account in a moral assessment of someone who breaks the commitment to be sexually faithful. In the final section of the paper, I will discuss how the dominance of the norm of monogamy might be taken into account when assessing how wrong an instance of sexual infidelity is.
There is the further complication that the commitment to be sexually exclusive is often not made explicitly, with there being no commitment formally made, and couples merely assuming that it is implied by the conventions of the sort of relationship they are in. Even if they have made an explicit commitment, they might not have not discussed what the purpose or meaning of the commitment to be sexually exclusive is or if there are any cases in which it is ok to break it. This is strange for something so significant that it could cause their relationship to end. Without really understanding the purpose of a commitment, it is difficult to assess how wrong it is to break it. Suppose Chloe makes a commitment to Sarah that she will give up drinking. There are many reasons for which she might do this. She could be converting to Islam; she could be an aggressive drunk; she might need to lose weight; it might just be that Sarah does not like her drinking. The reason why she breaks the commitment is also crucial to how we assess the morality of what she's done. She might have changed her mind about converting to Islam; she might be toasting her sister's wedding; she might be drinking purely to annoy Sarah. Therefore, the broken commitment will have a different significance to their relationship, depending on why she made it in the first place and on why she breaks it.
Similarly, there are various reasons why a couple might commit to be sexually exclusive: They might be doing it for religious reasons; they might be married and believe that marriage is necessarily monogamous; they might be too jealous to be non-monogamous; they might do it to express their love for each other. They might also just be monogamous without really considering why. If the purpose of the commitment has not been reflected upon, or discussed, it is difficult to make a full moral assessment of what breaking it entails. It could be that the person who was sexually unfaithful simply did not think sexual fidelity was that important, or perhaps they assumed the relationship was non-monogamous. This is part of the reason why sexual infidelity might be taken more seriously in marriage, if exclusivity forms one of the marriage vows then it is clear that it is an expected and significant feature of the marriage, but even then, the couple might not have thought about why monogamy is an expected feature of marriage and what significance it will have to them.
Thus, the obligation to be sexually exclusive is more significant if the couple in question has discussed, negotiated, and freely committed to being sexually exclusive for reasons important to them. It is, therefore, easier to assess why an instance of sexual infidelity is wrong, and, indeed, the wrong is likely to be more serious (all else being equal) when an explicit commitment has been broken. This can be a reason why sexual infidelity in polyamorous relationships, which generally involve more explicit communication about the boundaries of the relationship and the feelings of those involved, might be experienced differently (and perhaps as worse) compared with when it occurs in monogamous relationships. In any case, in order to work out whether the commitment to be sexually exclusive might be particularly important, we need to consider the significance of sex and sexual exclusivity, to which I now turn.

The sexual part of sexual infidelity
If there is to be something distinctive about sexual infidelity, as opposed to other kinds of broken commitments, it will have to be because of the meaning or significance of sex. One approach would be to argue that to have emotionally insignificant sex outside of a relationship would be to show that the sex within the relationship is also emotionally insignificant. Fiona Woollard and Bryan Weaver advance this kind of view, arguing that the requirement of monogamy is justified if both partners see sex as being tied to emotional intimacy in general and if they decide to limit their relationships of erotic love to one. If they see sex in this way, then 'sexual activity becomes conceptually inseparable from the kind of emotional intimacy that is associated with erotic love' and 'sexual activity without this emotional intimacy is hurtful to the other spouse' (Woollard and Weaver 2008, p. 515). If partners see sex in this way, then for one partner to be sexually unfaithful will be hurtful to the other. This is because either the unfaithful partner has been emotionally intimate with someone else in a way associated with erotic love (and, therefore, presumably, their love for their partner is not exclusive) 10 or because they have shown, through having non-intimate sex, that the sex they have with their partner does not have such significant emotional importance. This is because, their non-intimate sex shows that, for them, sex is not 'conceptually inseparable' from emotional intimacy.
Although I think that Woollard and Weaver are right to acknowledge that any justification for monogamy will need to make reference to the significance of sex to the partners, I do not agree that it is reasonable to assume that one's partner having non-emotionally significant sex with someone else entails that the sex within the relationship is any less significant, and so I do not think the justification is quite right. It seems unreasonable to presume that a person is psychologically incapable of having sex, which is loving and intimate in their long-term relationship but not loving and intimate in another scenario, such as in our example of Sarah's one-night fling in Rome. Woollard and Weaver observe that their justification for monogamy relies on it being reasonable to attach emotional significance to all sex. However, they also acknowledge that there are different ways of conceiving of sex, and that not all spouses will conceive of (all) sex as being connected to emotional intimacy. They suggest that if spouses do not conceive of sex outside of the relationship to be emotionally significant, then this way of seeing sex is compatible with non-monogamy (Woollard and Weaver 2008, p. 516).
However, if there are different ways of conceiving of sex, it seems unreasonable for a person to refuse to acknowledge this and to instead choose to attach a single meaning to all sex acts. If sex can have different levels of significance, it is conceivable that it could have different levels of significance to the same person in different circumstances. Therefore, seeing the sex you have with your partner as emotionally significant does not automatically entail that the sex you have outside of your relationship will also be emotionally significant. Furthermore, having emotionally insignificant sex outside of your relationship does not imply that the sex you have in your relationship is any less significant to you. It might have this implication; the sex you have had with another might make you realise that you do not care much for your partner or for the sex you have with them. However, it could also make you realise how much you love your partner and make the sex you have with them even more emotionally significant to you.
In addition, Woollard and Weaver do not discuss cases where one partner changes their mind about the significance of sex or when they have never agreed. It is likely that many couples have different views about the significance of sex, and even when they do share the same view, there is always the possibility that one of them (but not the other) will change their mind. Suppose Clive and Jemima both believe that all sex is emotionally significant. They thus decide to be monogamous because they assume that to have sex outside of the relationship would imply that they loved the person with whom they had sex, and they do not want any additional relationships of erotic love. However, one night, Clive has drunken meaningless sex at a party with Francine, and realises that sex can have different meanings as he still finds the sex he has with Jemima to be emotionally significant. Jemima might be reasonably hurt, for many reasons, at his transgression here, but it would be unreasonable of her to insist that the sex Clive had at the party entails either that he loves Francine or that the sex he has with Jemima means nothing.
Nonetheless, there is an indisputable way in which the sex between Clive and Jemima has changedit is no longer exclusive. Thus, in order to examine why sexual infidelity might be wrong, rather than focussing just on the significance of sex to the couple, we need to look at the significance of sexual exclusivity. As I said above, sex when exclusive might be a very different experience to someone compared with non-exclusive sex, and so when someone has been deceived into thinking they are having exclusive sex, this is particularly problematic. However, even if there has been no deception, the person cheated on might feel wronged, and reasonably so, because they have had no say in the decision to make the sex with their partner nonexclusive, and this might affect the way that they feel about the sex they have with their partner. If agreeing to have sex exclusively was a decision they made together, the decision for their sex to no longer be exclusive ought to be made together too.
As I will now argue, a commitment to be sexually exclusive might be made for good reasons. Below, I summarise my views as to why, for some couples, the commitment to be sexually exclusive might be important, reasonable, and compatible with love.
First, sexual exclusivity can be a way to try to maintain love by keeping partners together. Sex can lead to love, or to the redirection of one's attention, and so prohibiting sex outside of the relationship can be a way to try to hold the relationship together, providing a degree of security to the couple. One simplistic way that sexual exclusivity maintains love is because, as Wasserstrom puts it, 'if one consequence of being married is that one is prohibited from having sexual intercourse with anyone but one's spouse, then the spouses in a marriage are in a position to provide an important source of pleasure for each other that is unavailable to them elsewhere in the society' (Wasserstrom 1998, p. 149). However, as Wasserstrom highlights, this sort of explanation is not necessarily an argument for the immorality of adultery, for it merely shows that sexual exclusivity can have an instrumental role in holding relationships together (Wasserstrom 1998, pp. 149-150). If Sarah decides that sexual exclusivity is not having this instrumental role, perhaps it is, instead, likely to make them break up, because she wants so much to try sex with a different person, then, by this explanation of the importance of monogamy, it seems that perhaps she ought to sleep with someone else.
However, the role of sexual exclusivity in a relationship might maintain love more than just instrumentally. It might have an expressive and symbolic function too. Loving relationships are hugely important to us, but are also fragile, and we are vulnerable within them because we care about the other person, and their evaluation of us, but we cannot directly control how they feel, or indeed, even know how they feel for sure. In addition, we know that our partner could leave us at any time. Because of the difficulty in knowing how one's partner 'truly feels', as well as the oft-cited difficulties people have expressing how they 'really' feel to their partners, people often use expressive or symbolic action to help. Certain actions or sacrifices can help to show how significant someone is to us, and there are societal conventions that help us to do this. Setting aside certain activities to be shared exclusively is one of the ways that we can show strongly how much another means to us (McKeever 2017, p. 372). Sex has various qualities, such as being intimate, pleasurable, and involving vulnerability and care, that make it a particularly appropriate vehicle for expressing love, as well as a means of building love (McKeever 2016). People also tend to see it as a valuable part of a romantic relationship, as Woollard and Weaver rightly acknowledge. Thus, a couple might choose it as an activity to share exclusively as a symbol or expression of the strength of their exclusive love for one another (McKeever 2017). If a couple see sex in this way and have agreed to share it exclusively as a way to show to each other and to third parties how important their relationship is, then there does not seem to be anything unreasonable about them making the commitment to be exclusive or to agreeing that a decision to change the agreement should be a decision they make together.
Thus, if the couple have explicitly agreed to be sexually exclusive, and for this exclusivity to have a symbolic or expressive function, then for one partner to be sexually unfaithful is wrong, and the person cheated on is justified in feeling hurt. They are breaking a meaningful agreement without the consent of the other in the context of a relationship in which both partners are somewhat vulnerable. This might be one reason why we see sexual infidelity as a distinct kind of infidelity. However, it is not necessarily worse than some other kinds of infidelity in a relationship; neglecting one's partner, for example, is also a kind of infidelity, in that the neglectful partner has broken an (implicit) agreement to attend to and care for their partner (McKeever 2017, pp. 364-366). Furthermore, as the previous discussion has shown, the morality, or lack thereof, of sexual infidelity becomes much murkier when there has been no explicit agreement over what sexual exclusivity means to the couple. In addition, if the couple does not have sex, and have not done for a long time, then it is much more difficult to give an account of what is wrong with one of them having sex with someone else that does not rest purely on jealousy or their exclusivity being an instrumental way to keep them together. Finally, as Liberto highlights, sexual exclusivity is not necessarily the best way to communicate love (Liberto 2017, p. 412). Indeed, its expressive and symbolic function will depend, not only on the wider culture in which the couple lives, but also on various other factors, including their own personalities and values, and their views on sex are likely to change over the course of their relationship. Therefore, although partners might be justified in being hurt over sexual infidelity, it is not, in all cases, as serious as wrong as it is sometimes taken to be, and we should be much less hasty in condemning adulterers without knowing the full situation. In the next section, I will discuss how the norm of monogamy contributes to both the prevalence and pain of monogamy.

Sexual infidelity and the norm of monogamy
So far, I have tried to provide some clarification over when, why, and to what extent, sexual infidelity might be wrong. I have argued that it is prima facie wrong to deceive one's partner about sexual infidelity and prima facie wrong to break an explicit commitment to be sexually faithful. However, I have also shown that the situation is complicated. To fully understand sexual infidelity, and why it hurts so much, we need to consider the context in which it happens. It occurs within a culture that has certain standards, norms, and values for what types of relationship are acceptable and what these relationships should be like. Historically, adultery law favoured men over women. For example, in England until 1923, although men could divorce their wives on the basis of a single act of adultery by his wife, a husband committing a single act was seen by the law as 'a regrettable mistake' (Vitiello 2017, p. 315).
Moreover, in most Western, mainstream societies at least, there is a hegemonic norm of monogamy that governs romantic relationships. It is especially important to acknowledge this norm because many relationships involve only a tacit commitment to be monogamous and the relationship is assumed to be monogamous because it is the type of relationship governed by the norm of monogamy. This norm is both a cause and a consequence of the widespread, yet false, belief in two hypotheses that Carrie Jenkins identifies as 'moral monogamy' and 'modal monogamy'. Moral monogamy is the hypothesis that 'the only morally permissible romantic love relationships are monogamous ones'. Modal monogamy is the hypothesis that, 'the only metaphysically possible romantic love relationships are monogamous ones' (Jenkins 2015, p. 175). The hegemonic norm of monogamy has also been called 'mononormativity'. In what follows, I show how the hegemonic norm of monogamy increases both the prevalence and pain of adultery, through decreasing people's options to be consensually non-monogamous and promoting ideas, such as that sexual infidelity is a sign of a lack of love, which make sexual infidelity more painful when it does occur.

THE HEGEMONIC NORM OF MONOGAMY MAKES IT VERY DIFFICULT TO PRACTISE CONSENSUAL NON-MONOGAMY
If you want to have a particular kind of intimate relationship that involves love, sex, commitment, a shared life, it is very difficult, in most Western mainstream cultures at least, to find this unless you are prepared to be in a monogamous romantic relationship. In addition to being mononormative, our society is, as Elizabeth Brake calls it, amatonormative: we prioritise romantic love over other kinds of caring relationship (Brake 2012). Although people, of course, have caring relationships that are not romantic, such as friendships and familial relationships, Brake argues that the societal assumption 'that the most valuable relationships must be marital or amorous devalues friendships' (Brake 2012, p. 5). Therefore, it is difficult to access all the goods that come along with caring relationships outside of a romantic relationship, and it is difficult to have a romantic relationship that is not monogamous. This is not to say that we should abandon monogamy or romantic love. Many people find great value and purpose in being in a monogamous romantic relationship, and many people are sexually and emotionally satisfied by monogamy. However, it is also likely to be true that people have different dispositions regarding sex and that some people will find that they are unfulfilled by being permitted to have sex with only one person for their whole life.
It is, of course, possible to be in a polyamorous relationship, and some evidence suggests that people are becoming more tolerant and open to such relationships. 11 However, many people will not find that this is a realistic option for them. Polyamory is still stigmatised, and many people have negative associations with any kind of non-monogamous arrangement. For example, some people might assume that the alternative to monogamy is promiscuity, sexual infidelity, or polygamy, which they associate with polygny and oppression to women. Polyamorous people are sometimes seen as obsessed with sex, selfish, immature, or 'unable to commit'. Even putting these negative associations aside, many people do not believe that polyamory 'works'.
A survey carried out by Marisa Cohen in 2016 suggests that people perceive monogamous couples to have higher relationship satisfaction than people in polyamorous relationships (Cohen 2016). However, a review of research, exploring the associations between consensual non-monogamy, psychological well-being, and relationship quality, found that polyamorists and monogamists have similar levels of psychological well-being and relationship quality (Rubel and Bogaert 2015). This suggests a disconnect between many people's perception of how polyamory works and how it actually works.
Even if you are willing to put up with the stigma, it is hard to meet people who want a polyamorous relationship, and society, with its focus on 'the couple', is not well set up for people in polyamorous relationships. If you are in a monogamous relationship, as mentioned earlier, it is not always possible to ask for a non-monogamous arrangement without making your partner feel rejected. For some people, for their partner to even suggest this would seem like a betrayal and could spell the end of their relationship (McKeever 2017).
None of this justifies sexual infidelity, but it does give us some insight into why it is so common, and why deception often goes along with it. Sex and love are two of the most important things in many people's lives, and if the only way that we can access them is via a monogamous romantic relationship, but such relationships are notoriously bad at providing long-term sexual (and also often emotional) satisfaction, then unsatisfied people have three options: (1) stay in the relationship without being fully satisfied, (2) break up, or (3) commit sexual infidelity. None of these are ideal. If it was more socially acceptable to practise consensual non-monogamy, there would be a fourth option open to people in relationships which are not fully satisfying. This could allow people to remain in their relationship without betraying their partner and could ultimately lead to greater overall satisfaction for both partners.
Breaking up is often not an option for all kinds of reasons, some emotional and some practical, and undoubtedly, many people stay in long-term relationships that are not sexually satisfying to them. Indeed, a study carried out in 1994 of 3159 Americans aged 18-59 found that almost 15% of married people had not had sex in the previous year (Laumann et al. 1994). A qualitative study carried out in 2008 looking at how people in sexless marriages or long-term relationships feel found that many felt frustrated, depressed, or rejected. For example, one man said 'it has a deleterious effect on my overall life. I dwell on sexual thoughts and fantasies. I am depressed. My professional life is impacted … This detracts from the time I should spend on work related activities.' Another woman was quoted as saying 'I'm depressed and frustrated, I don't feel worthwhile anymore' (Donnelly and Burgess 2008, p. 528). However, most wanted to stay in their relationships, speaking of shared commitments and love for their partner holding them together, although 26% had had an affair (Donnelly and Burgess 2008, pp. 531-533).
In addition to people in sexless relationships, there are numerous other people who are having sex, but find it unsatisfying, or who would simply like to have sex with other people. While sexually exclusive sex in a loving relationship is valuable and may be felt to be important, there is a kind of value that can be found in having sex with someone new that cannot be found in a long-term relationship. The new person chooses you as a person to have sex with. They do not have sex with you to express love, or because they have committed to have exclusive sex with you. This can provide a sense of validation, a feeling of being desired and recognised. The sex might also be of a different kind to the sex you have with your primary partner. As Mike Martin notes 'many people find joy in extramarital sex, and for some the joy may be the greatest they find in life'. He also highlights how 'some marriages are sexually frustrating or damaging in other ways to self-respect' and 'more than a few individuals report their extramarital affairs were liberating and transforming' (Martin 1998, pp. 160-161). This is not a trivial matter. A large number of people are unfulfilled and unhappy in monogamous relationships, some of whom are dealing with that lack of fulfilment through sexual infidelity, which might hurt their partner, and create feelings of anxiety and inner conflict and ultimately could lead to the end of an otherwise strong and important relationship. Adulterers are often vilified and ostracised from social groups, and people cheated on often lose confidence and feel humiliated. Although, of course, unfaithful partners are not blameless, sexual infidelity would no doubt be less prevalent if there were more realistic options to engage in consensual non-monogamous arrangements.

THE HEGEMONIC NORM OF MONOGAMY MAKES SEXUAL INFIDELITY HARDER TO DEAL WITH FOR ITS VICTIMS AND FOR ADULTERERS
Not only does the cultural dominance of monogamy probably make sexual infidelity more widespread, but it also likely makes it into a more painful experience for all involved when it does occur. It does this, first, by making unfaithful partners much less likely to be honest about their infidelity, compounding the wrongness of their infidelity with deception of their partner, and making it more hurtful if it is found out. Second, the norm of monogamy leads some people to believe that sexual infidelity must have 'meanings' and significance that it might not in fact have to the person who has committed the infidelity. This can lead to divergences in understanding between the unfaithful partner and the person who has been cheated on. For example, people who have been cheated on often take their partner's infidelity to be an indication of their partner no longer loving them, or having never 'really' loved them. Another commonly held view is that being cheated on shows that someone is not 'enough' for their partner. 12 These ideas are related to 'really love' someone is sometimes thought to mean that they are 'enough' for you, an idea promoted by the norm of monogamy. As Erik Jansson Bostrom puts it, there are 'two interconnected ideas from the monogamous worldview: first of all, the idea that two people can be enough for each other. Second, that two people should be enough for each other' (Jansson Bostrom 2017, pp. 91-92). Thus, if your partner is not 'enough' for you, then you do not really love them. Rather than sexual fidelity being seen as supportive of love, it becomes equated with it.
However, when questioned about their sexual infidelity, people who have been unfaithful give a number of different reasons why they did it, many of which are not to do with love. A large-scale review of studies on infidelity by Adrian Blow and Kelley Hartnett revealed a number of reasons people give for cheating, including relationship dissatisfaction, sexual dissatisfaction in the primary relationship, opportunity, curiosity, desire for excitement, having a more permissive attitude towards infidelity, and wanting to get even with a spouse (Blow and Hartnett 2005). A survey by Glass and Wright found others, including 'for fun', 'for intellectual sharing', 'to feel young', 'for novelty and change', and 'enhancement of confidence and self-esteem' (Glass and Wright 1992, p. 372). However, people who commit sexual infidelity might find that the reasons they give for their infidelity are not believed, because the mononormative culture, with its widespread belief in both moral monogamy and modal monogamy, allows sexual infidelity to have only certain meanings. If we lived in a society with a culture that did not equate love with sexual fidelity, or promote the idea that, in love, one person can and should be 'enough' for another, people might be more willing to accept that sexual infidelity need not entail a lack or a loss of love.
Furthermore, being cheated on can feel shameful and humiliating, again because of the mistaken idea, promoted by the norm of monogamy, that to be cheated on means you are not 'enough' for your partner but that you should be. It can thus be erroneously taken to imply that there is something wrong with you. This adds to pressure on people who have been cheated on to end the relationship, despite how much further pain that will cause, rather than forgive their partner, even if that is what they really want to do (McKeever 2017, pp. 364-365). It can also be seen to be a matter of pride; staying with an adulterous partner can make others think that you lack self-respect, that you do not think yourself good enough to be with someone for whom you are 'enough'. Again, this idea is promoted by the norm of monogamy.
Therefore, in many cases, monogamy norms increase the contingent harms of sexual infidelity by increasing the likelihood that it will involve deception and by increasing the hurtfulness of it by leading people who have been cheated on, and those around them, to believe that infidelity means things, such as that the unfaithful partner no longer loves their partner, when in fact this might not be true. In a society which that not equate love with sexual fidelity or promote the idea that one person can and should be 'enough' for another, there would be fewer misconceptions about what infidelity entailed about the attitudes or feelings of the unfaithful partner, and people who have been cheated on would be less likely to feel humiliated or suffer a loss of pride.

Conclusion
In this paper, I sought to get greater clarity over the wrong of sexual infidelity. I began by exploring how we might conceive of the wrong. First, sexual infidelity usually involves hurting one's partner. I argued that, although the hurt caused should be taken into account when assessing sexual infidelity, it does not provide us with a full explanation of why it is wrong, and it might be better conceived as evidence for the wrong, rather than being constitutive of it. Second, sexual infidelity often involves deception, and this deception is particularly serious because it can constitute a kind of free riding if the other partner is playing by the rules on the assumption that their partner is, but also because it could undermine sexual consent. However, it seems that it is the deception, not the sexual infidelity, which is doing the wrong-making work here, and it is not clear that infidelity with deception is always worse than infidelity without deception. In any case, as not all sexual infidelity involves hurt or deception, and so neither is an essential feature of it, I focussed my exploration on commitment-breaking and the sexual nature of the broken commitment. Sexual infidelity is, at root, an infidelity, that is, a broken commitment, and the commitment is about sexual exclusivity. I considered in more detail what breaking a commitment to be sexually exclusive amounts to, arguing that there can be good reasons to commit to be sexually exclusive, and reasons to be hurt if one partner unilaterally decides to break this agreement. However, it is not clear that sexual infidelity should be seen as worse than other kinds of infidelity, and the situation becomes even harder to assess when no explicit agreement has been made. This is why a discussion of the rights and wrongs of sexual infidelity needs to acknowledge the context in which it takes place, and, in particular, the role that the hegemonic norm of monogamy has in both the prevalence and the pain of monogamy. Sexual infidelity might not occur so much were people able to be more honest about their desires with their partners, and if there were more realistic opportunities for people to engage in consensual monogamy. And, were the norm less stringent, when sexual infidelity did occur, it might be less painful and more easily dealt with.
Nonetheless, as I said at the beginning, all this is assuming that the relationship in question is equal, and that there are no aggravating factors accompanying the sexual infidelity. I hazard that, more often than not, sexual infidelity occurs alongside other serious wrongs and in nonideal relationships, and so, in practice, the moral assessment of an instance of sexual infidelity would need to take these other factors into account.
2 I thank an anonymous reviewer for helping me to clarify this definition. I acknowledge that there are arguments, such as those of Michael Wreen (1986), which claim that marriage is necessarily monogamous, and so even consensual non-monogamy is wrong. I do not discuss this kind of argument here, as I want to focus on relationships in which there is an agreement to be monogamous. I will assume in this paper that consensual non-monogamy and polyamory are both possible and not morally troubling.
3 Incidentally, the UK legal definition of adultery specifies that adultery is 'sexual intercourse between a consenting man and woman when at least one partner is married to someone else', thus entailing that people cannot get a divorce on the grounds of adultery on the basis that their partner had sex with someone of the same sex as them. 4 The Office for National Statistics data from 2015 shows that marriage rates are now at their lowest level ever and have been declining since the 1970s (Haines 2015). 5 For an interesting discussion of the problems with using ideal theory in ethics, see Mills (2005). 6 For an account of lying as manipulation, see Faulkner (2007). 7 Although he does not explicitly discuss sexual infidelity, Tom Dougherty argues that deceiving someone into sex is a serious moral wrong, as it vitiates their consent to sex (Dougherty 2013). 8 Woollard and Weaver (2008) discuss how sexual infidelity might be considered a denial of the value of the sex in the relationship. I discuss their account in more detail below. 9 We might also note that sexual infidelity might not involve only the breaking of the commitment to be sexually exclusive; it might also, for example, involve breaking the commitment to tell your partner everything, or to never deceive them. 10 I am reminded here of Steinbock's claim that 'sexual infidelity has significance of a deeper betrayalfalling in love with someone else' (Steinbock 1986, p. 14). 11 A recent study using two separate US Census-based quota samples of single adults in the USA (over 8000 people in total) found that 21% of Americans have engaged in some form of consensual non-monogamy in their lifetime (Haupert et al. 2017).
12 This is a fairly common view found in advice columns, popular magazines, and internet blogs. See, for example, Engle (2015).