It sucks that you had to deal with that. I don't know exactly how you feel, bc when that happened to me, I was only dating my bf, I hadn't been married to him. BUT, please, PLEASE don't let this get you in a rut. Don't fall into an episode (what I like to call them). You are SOOOOO much better than they are. He cheated, he lied, he gave you a disease, for crying out loud!!! He is a piece of trash, it sounds like to me, and if he's that, that makes her even worse for wanting to be with him. You are finished with him, relationship-wise anyway, although he is still the father of your son, but there is nothing between the two of you. I know it's hard, but he's going to do whatever it is that he does, which probably entails dissing you (at least that's what happened to me), and, so, let him. Everyone who has a brain cell in their head will know better than listen to anything the two of them have to say. Your closest friends and family are the ones who matter, not them or anyone who associates with them. It took me a long time to realize this (over a year or paranoia and anger everytime I thought about it or saw them), but I am better for it. I let go. I realized than my ex was soooo stupid for doing what he did and nothing I did was going to change that. The only thing I lost out of the deal was baggage. I still hate him for doing what he did, but I don't get angry. I chock it up to stupidity on his part. I'm not saying you can't install a punching bag in every room in your house (or car), but you are so much better a person than either one of them. If you don't want to let it go, move past it, and just go back to it when you want to knock someone's lights out.