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.