Who needs friends like that. Seriously you can do better. If I was a wife in a group of friends like that, I would be worried about what my husband is doing also. Birds of a feather as they say.
I agree! Ugh, who need friends who will believe a cheater's lies and tell you you should stay with someone who would cheat on you?!?
My XH didn't cheat, but he is a sh!tty, sh!tty person. He pretended to be a completely different person (from his true personality) to get me to fall in love with him, and he was emotionally abusive/manipulative throughout our relationship. When the facade of his fake personality began to fall away, I learned that he was the type of person that I would never normally associate with--and I was married to the guy! I wanted nothing to do with him, and I would never be friends with someone like him. I'm lucky in the fact that we had no kids, and I was able to walk away cleanly.
He also told lies about me to all our mutual friends, and they believed him. So I'm not friends with them anymore, either.
OP, you are under no obligation to be friends with your XH, especially not after he cheated on you. If you have kids, maintain an amicable but business-only relationship for the benefit of your kids, but you don't need to do anything more than that.
ETA: Just went back to original post. I see that you don't have kids with him, but your younger ones like him and want to see him. I would keep that to a minimum, if you can. I wouldn't want my kids looking up to a cheater or viewing him as a role model. But kids do get attached. Since he's not their bio dad, I don't really know how to advise you on this. I mean, you're the adult. You're the one in charge. Helping them maintain a relationship with him isn't good for you, and if you don't want them to see him, well, that's your decision. You can explain it when they are a little older, I suppose.