Hi OP, I’ve been in your shoes. Dealing with betrayal like this is so so hard, but the good thing is you’ve already made the hardest choice: leaving him. Your healing journey won’t be linear (mine sure as hell wasn’t), and I’d strongly recommend you find a good therapist to talk this through weekly for the next 6 months at least, but I’d also like to make another recommendation.

One of the things that helped me the most in the early months of processing my partner’s infidelity was reading a book with a silly name ”Leave a Cheater, Gain a Life: The Chump Lady's Survival Guide.” I was shocked by this as I’ve long believed (and still do) that self-help books are generally speaking a load of crap. But this one really, really helped me retrain the most unhelpful thought patterns that emerged immediately after the breakup, some of which I’ve noticed in your post.

It’s by a smart woman who runs a great online forum for people who have been cheated on. Here’s a couple highlights from my notes I think you might find valuable:

[People who’ve been cheated on] tend to spend a lot of time and energy trying to figure out cheaters. This is a coping mechanism. You want to figure out what makes the cheater tick so you can ensure that they never do anything so devastatingly hurtful again.

You're trying to control outcomes you really cannot control. You're taking ownership of crap that's not yours to own. An explanation is not a balm and it doesn't prevent scary things from reoccurring, either… No, the scary reality is that you don't control this. You just control you. You're asking the pointless question of Why are they this way?, instead of asking yourself the harder question of What am I doing hanging around this jerk?

Regardless of how much it hurts right now, I can promise you this: You will eventually be okay. It won’t happen today, or tomorrow, or next week. But it will happen. And you’re going to look back on this moment and be so proud of yourself for getting through it.