The "what if" cycle is a "looking back" task.
Kind of telling yourself that if you could only go back and do it again, you could make things perfect maybe.
Perfection. A life lived so that you could have controlled each and every outcome. Those "what if" thoughts are still about control. If only you could have controlled that moment, that unpredicted turn of events, that other person's decision, seen around that corner….
Thing is, we just can’t do any of that. But you already know that. There is no perfect life.
Maybe your lesson is "let go of perfection".
You have the ability to control one person in this world, and that is you.
I can only speak to my experience. In my FOO, I was afraid of making an error. Mistakes weren’t seen as a learning experience, they were deadly sins and met with violent repercussions. As an adult, I would punish myself for even the smallest error, berating my stupidity, telling myself how worthless I was. I was afraid to try new things, knowing I would fail at first - failing wasn’t a thing we were allowed to do as kids, and I feared that. It took time and personal growth to learn about failure as part of learning anything new.
I’m wondering if you are seeing his affair through the lens of "what ifs", and thinking things like "what if I had done x, then I could have prevented this"?
Because this is self-blaming. I did similar things. I think most BS do this. Thing is, your spouse made those decisions, each and every step of the way. The affair wasn’t one decision at one point. It was a series of decisions.
Just as reconciliation is a series of decisions. Take your time. It’s good work you’re doing right now.