Cheating is often assumed to occur when one person in a monogamous relationship does not tell their partner about a sexual affair. Yet, in practice, what does it mean to "cheat" in such a relationship? Does cheating happen if a person finds someone else attractive-the instructor, the bartender, the stranger on the street - and says nothing to their partner? Does cheating happen if one person develops a crush on another person, thinks about the other often, maybe even while having sex with their partner? Does the person have a responsibility to tell their partner about sexual fantasies involving others? Does cheating happen if one masturbates, watches porn, or talks with others on social/dating apps and the other does not know?