What would make you think they don't? Women are the "gatekeepers" of sex and that gate seems to have been broken down with the horses running wild for quite some time. For every guy having sex, there's got to be a girl with them. But that would be belaboring the obvious. I would be more curious to hear about whether "cheating" is overly negatively charged word compared to "supplementing". When people write about this stuff, it is as if we were in some "puritan" utopia - so shocking that someone would "cheat". If I told you that you could only have one friend and if you wanted to be frends with somone else then I can't be friends with you, would that be reasonable? Seems kinda "selfish" doesn't it? That really reduces or eliminates our personal freedom - doesn't it? It puts us in complete servitude and depenence on that person - doesn't it? Yet, those are the standards we hold our romantic relationships to. It's little wonder why infidelity is up, divorce is up and rates of marriage is crashing. All indicators are heading in the wrong direction - likely because we're all just too irresponsible to do anything that requires "work" against our natural inclinations.