Well, he's her problem now. Maybe you can, I dunno, let it accidently slip to her that he and you were married and living together when they first began having that affair?

Okay, maybe not the most mature route, granted, but satisfying none the less, right?

EDIT: Oh, and though I don't recommend doing the things mentioned in this song, it's fun to listen to nonetheless. Sorry if it's not to your liking, but it makes me think of the whole damned stinky situation your in and what's possibly on your mind.