@Else22,
Hang out with a different circle of friends. Or be busy. Or make yourself busy.
You're taking a class. You met a new guy. You're volunteering at a hospital. You're crocheting a freakin' afghan.
Find reasons to not hang around with him. And not just this week or this month, but more like this year.
If your family and friends ask, it is none of their damned business. But if you must craft a reason, use one of the ones I've provided above. Or, better yet, really do take a class or volunteer or whatever. Make it the truth.
Do good things, fun things, silly things, rotten things, whatever. But do them away from this man.
You are perpetuating a lie by hanging around and pretending everything is groovy. You are going to end up back in bed in a heartbeat, when the coast is clear. That is not a very nice thing to do with his wife who, I assume, you are at least cordial with.
BTW, news flash, regardless of what he claims, regardless of how many times he says, "love, love, love," he is not going to leave his wife. He is already using his kids as an excuse. He's just keeping you on the side, and wants to get into your pants again.
I'm sorry. I know I'm being harsh, and I am sorry, but I don't see a way to sugarcoat this. You are one half of a major league deception. Hanging around as if everything is wonderful and all is really just kinda hurtful. Plus - seriously - if you hang around, she will find out. She probably already suspects something. She will eventually put two and two together. And when she divorces him, gets custody of the kids, and takes him for all he's got, he's not going to look so attractive anymore. And he may very well blame you for the end of his marriage.
Do your future a favor, and really do get out and go after someone else. Because you won't do that if you're hanging around with this crowd. Do not build a friendship.
There is no friendship to build, because friends don't ask their friends to be a part of a big lie, and it's not very friendly to use someone for sex and play with their feelings, either.