not want your partner to cheat
IMO cheating is by definition something your partner does not want. Defining cheating as a certain set of actions that everyone agrees on independent of the relationship is a dead end. If you instead define cheating as “knowingly violating your partner’s boundaries” (and make sure to talk about those boundaries!), everything becomes so much easier
Kids will do stupid things sometimes, no avoiding that. In Germany you can pass a stopped bus on the other side of the road, but if it has its hazards on, you can’t go faster than walking speed.