No argument can sufficiently capture what it is that motivates someone to cheat. That is because each instance is unique, resting upon a complex of factors that no one but those involved can fully understand. To look at infidelity as a single category undermines the range of ideas it contains. As well as the range of people, their motivations and behaviours, that it claims to describe.
It is reductive to believe there is a single explanation for infidelity. This is simply untrue. Analysis must be made on a case-by-case basis. The reasons another person chooses to do anything are impossible to know. This is typified by the term "cheat", which itself can mean a number of things. Would we class a long-standing emotional affair in the same category as a sexually charged encounter, and how might our reading vary depending on the state of a person's existing relationship? Answering these questions is not straightforward, but it does point to a single conclusion. That is that without knowing the links between these disparate forms of infidelity, they should only be looked at as stand-alone examples.
Infidelity may be situational. But so are most real-world events, ranging from crime to divorce. That does not mean that more general conclusions can be drawn about these subjects. Rather, it reminds audiences to maintain a level of caution in how they read into things.
[P1] All cases of cheating are distinct [P2] There is no single reason for why cheating happens
Rejecting the premises
[Rejecting P2] We cannot rule out there being points of similarity across all cases of infidelity