ABSTRACT The essay attacks the convention that a person should at any period in their life have not more than one sexual partner. The issues of the care of children and the desirability of a shared household are here bracketed out. The main argument proceeds by seeing conflicts between the requirement of exclusivity in sexual life, authenticity, and the principle that sexual communion should be an expression of love. A general social inertia, defined by the possessive introversion of couples, means that individuals will inevitably sometimes have to choose between sexual solitude and cultivating a more or less artificial relationship. The ideal of a single, central relationship is criticised on the grounds that (i) in some respects it is not desirable and (ii) it is in any case unrealistic to suppose that we can choose to create such an ideal relationship at will.