Regardless of what you find on Google, surely you can see that it's mathematically impossible for men to be engaged in extra-marital sex significantly more often than women are. It's not an opinion--it's practically a theorem! The only wiggle room is that single women might be feeling free to sleep with married men, but that's hardly morally superior, is it? And it's unlikely. Men having affairs prefer married women because (at the risk of seeming crude) a married woman also has skin in the game. Self-report studies make me laugh. Men and women report having had wildly different numbers of sex partners in general, despite the obvious fact that the averages must be identical. Not similar--identical. Work it out--for every man engaged in a heterosexual sex act, there is one woman, and vice versa.