It's OK to rage. essential even... just not at them every time.
it won't do them any harm to tell them to FTFO every so often, and to show them how much you hate them for hurting you as much as they did, but try to remain as controlled as possible.
I find Ice Cold Fury is the best place to get to, shows that you wouldn't piss on them if they were on fire, but means you don't get to wear the Crazy Bitch Ex badge.
My ex was abusive, not adulterous, but the rage is the same somehow, it's a betrayal I think, the realisation that it was all about them and not us, and when we are left feeling beyond foolish, it hurts. As I said though, its not our fault they were bastards. They chose to do what they did, for whatever reason. My dad cheated on my mum when I was a teenager and ultimately chose his OW over the whole family. I don't speak to him anymore, there is no point. I know this stuff hurts like nothing else. betrayal is betrayal.
You are BOTH doing so well and I hope you can see that it WILL get just a little less gut wrenchingly painful day by day. You will get through this and you will both be stronger and better people on the other side of this.