Ashley Madison(.com) has earned several million dollars facilitating extramarital affairs online; however, the market determinants of online infidelity matchmaking have not been researched. The now-infamous customer data breach in 2015 provided a unique opportunity to analyze a large population of individuals (N=702,309) who paid to engage in extramarital affairs using Ashley Madison. Aggregating this sensitive data into spatial units, we measured the relationship between several theorized market determinants and Ashley Madison subscription and spending rates in major United States markets. We found income is the leading market determinant for internet-facilitated infidelity, indicating the service behaves as a luxury good; further, several characteristics related to infidelity at the individual-level were also significant, including the negative relationship between religiosity and infidelity. Strong regression model performance suggests these results are robust insights into the market for online infidelity-matchmaking.