One of the things I have noticed when it comes to men and women is how much a man feels violated if his wife cheats and engages in sex outside the marriage. Even if the man does it himself, it's always a lot more "evil/bad" when the woman cheats. Actually, if you look at other cultures, some cultures punish women by death if she is caught cheating, and some cultures actually remove the part of a woman that experiences sexual pleasure too.

I think this is a very deep primal thing with men where in most cultures this is considered the worst of crimes a woman can commit. Yet throughout history men had their wives and the women they cheated with outside the marriage. Men think about sex in a different light then women do and I think this is more about nature's design that remains to confuse and frustrate beyond one's ability to rationalize.