Thanks for the clarification. I took a peek at your other post to better understand why you're seeking advice on forgiveness. And yeah, there are a lot of articles expounding on the benefits of "letting go of anger and resentment," but few of them explain how exactly to do that. I suppose it depends on each person, what they need in order to make peace with the situation, but I'll explain how I do it, or how I attempt to do it.

So, a common theme in Stoic philosophy is to focus on what is in your control, and to let go of things which are not in your control, and I've found this very helpful in situations where I've been wronged. Don't dwell on past misdeeds; you no longer have any control over these things, nor do you have any control over your ex's actions in the present. However, you do have control over how you respond to them, what lessons you take from them, and even (to some extent) what emotions arise from their misdeeds.

If I were betrayed by a romantic partner, I would first try to remember that, if I feel no resentment towards him, then he hasn't really harmed me. He's only really succeeded in harming himself, for his wrongdoings have caused his relationship with me to fail. By realizing this, I'm able to let go of that resentment, and then I can begin to see things a little more clearly. It's kind of a weird process because it requires some tricky introspection and cognitive gymnastics.

Once that fog of anger has passed and I can see the issue more clearly, I can respond in a much more effective way. And that's the goal, ultimately, to be able to respond in the best way possible. Anger often gets in the way of that and leads us to do things we regret, which is why we try to let it go as often as possible.

So, basically, focus on the ultimate goal - what can you do to respond to this situation in the best way possible? Maybe that's confronting him about his behavior with a stoic attitude, so that you can clearly tell him where he is wrong (what he does with that information is on him). Maybe it's simply understanding why he's done the things that he's done, perhaps so you're more prepared for such behavior in the future, either from him or others.

I also try to understand that there are no monsters in this world. Seeing him as a monster makes him bigger and more intimidating than he really is, like he's unstoppable, like he has no weaknesses. But he's just a man.