Why is it Worse When a Wife Cheats?

The movie is told from a man's perspective as he dates several women. During the course of the movie he meets, falls in love with, and then breaks up with one woman. While he dates and beds various other women, he becomes obsessed with the possibility that his former girlfriend may have sex with someone else.

After a passionate night of sex with yet another woman, he convinces his former girlfriend to meet him. When they do meet he demands that she tell him if she has had sex with someone else. At first she won't answer but he keeps demanding to know and she finally answers "yes." He storms out of the restaurant, furious that she has been "unfaithful" to their relationship.

Does the fact that he has had sex with several women since their break-up count for anything? Why is it okay for him and absolutely horrible for her?

I get emails from men whose wives have cheated on them. They want details, they demand details, they feel it's their right to know all the intimate details. And, even if their wives give them details, they don't believe the affair has ended. They're the same men who have been unfaithful in their marriages and some may still be cheating.

Here's an excerpt from one such email: "When I start talking about it I only see how bad I was hurt and humiliated. She did this in front of all of our family while I snuck around with people no one knew but me."

This man's wife had an affair with someone she'd known for a long time. The affair happened well into their marriage, long after her husband began his series of affairs. In an earlier email I said to him: "You are trying to make hers the greater sin. Adultery is adultery regardless of why it's done or who it's done with. You were wrong. She was wrong." This wasn't the answer he wanted.

Why is her cheating so much worse than his? Why is any wife's cheating so much worse than her husband's cheating?