MO Diver:Except maybe the innocent wife when she has (probably) unprotected sex with someone she thinks it's safe because she is married to him?
Salient point. The wife deserves to know. One way or the other, she will eventually find out. Better now than later. If he quits seeing your friend now, he will find another woman later. How should the wife find out? That's a tough one, and I'm not sure. I'm leaning more toward the camp that says to back off- vermin generally breed more vermin. A loser like him will do something stoooopid soon, and get busted.
I would like to say that your friend deserves better than this guy, but she's no better than him. She's using him just like he's using her. She knows he's married and doesn't plan to leave his family- as others have stated, a cake & eat it, too kind of guy. She knows he's married and neither of them have regard for the children and wife. Of course, she doesn't really owe the wife any alliegance, but the husband damn sure does.
Honestly, I couldn't hang out with your friend. I'm not judging her or you, but I would back off of her until she either comes to her senses, gets dumped, or ends up testifying in divorce court. I don't think you'd be a bad friend by putting space between you- in case you haven't noticed, it's all about her, anyway. How sad that she isn't willing to make the effort to find a nice, single guy. Contrary to popular belief, they are out there.
Foo