Monogamy is a hotly contested practice. In many cis-gender marriages, engaging in sexual intercourse with a non-spouse is regarded as a serious betrayal. But during some periods in history, it was not only accepted but expected. 'Philanderers' are now portrayed as suffering from 'sex addiction'. What do these shifts reveal about gender and sexual relations? Has the proliferation of sexualities and genders, together with rapidly changing sexual mores, dealt a death blow to monogamy? Or is it stronger than ever?