Beat the **** out of 'em, tell his wife and then dump him
That happened to me and luckily it was just two dates. I recall telling him that he must think I am a loser or something because only a loser gets involved with a man who is attached and only a loser cheats on his wife.
Ask myself what kind of narcotic made me date a guy first of all
I'd have a talk with him about that & tell him our relationship is not going to work.
Break it off. If he's cheating on her with me, then he is probably cheating on me and her with a 3rd unknown girl. I may consider giving him an ultimatum to tell her but I wouldn't expect him to pick me.
As for telling her myself, people shoot the messenger. I would let it go. Chances are she has an idea or she will have an idea eventually. I made out with a guy who was dating someone back in high school (over 6 years ago) and I learned quickly people blame the messenger.
I would feel sorry for his wife, and continue to **** him
I'd be like "..... WTF!?!? You're a GUY!?!?"