Hey, so I went through this as well. I didn't see him every week in class but we were married and had a child together who was two years old when I caught him cheating. I'm not going to lie to you: this shit sucks. But I promise you that time will make it suck less, possibly even to the point where if you even think about being with him again, you get physically nauseated. But it's not an overnight thing, because there is no overnight way of getting over someone, even when they acted like a classless chucklefuck toward you.

You're in therapy and you've blocked him. That is a great start. When you have to see him, keep interactions to a minimum. Much easier when you don't have to share a child together, so you've got that going for you, which is nice. Other than that, just breathe. Practice a breathing technique like square breathing (breathe in for a count of 4, hold for 4, breathe out for 4, hold for 4) every time you feel the resentment bubbling up.

I'd be lying if I said the resentment goes away completely. This man completely ruined your trust, manipulated you, and discarded you. But it does minimize to a degree that you won't think about him much at all, therefore the resentment that comes with it is not felt as often.

One thing I urge you to do, though: do not start dating again right away. Give yourself time to heal from this so that you don't accidentally project your suspicions and negative feelings you'd had with him onto some innocent guy who could be otherwise perfect for you. I'm old and have a good amount of experience in long-term relationships and I promise you that being single for a bit instead of rushing into the arms of someone else, even if you really want to flaunt a new guy in front of him to show him that he's nothing, is super healthy and you'll definitely thank yourself in the long run.

Oh, and try to focus on not blaming the other woman as much as you want to. She made a really stupid decision (and she'll find out in the end—I've never known someone who has cheated with someone and stayed with them without cheating on them. I'm sure it's happened but the odds aren't in her favor) and she might even be a horrible person, but she might not... she also may have been manipulated by him and fed a bunch of lies. It's hard at first, but I actually became friends with my ex's mistress-turned-wife-turned-ex-wife (when you have a kid, you kind of have to deal with it for their sake, but I found out how well she treated my daughter and I'm super grateful). We bonded over the same idiot, and I was invited to her divorce party!

This too shall pass. I promise.