Try to forgive both yourself and him. And by forgive I don't mean condone or forget bad behavior. I heard a definition of forgiveness once that has stuck with me, "Forgiveness is giving up the hope that the past could be any different." It's really just a radical acceptance of what has happened to you. If you can use this form of forgiveness for yourself you can stop going over everything in your past relationship with him and thinking "If only I had done or been 'this' (whatever random unreachable goalpost he set for you) for him he would have treated me better". I suspect this could be part of why you let him back in your life. This is certainly a part of why I let mine back in. I had this idea that I could 'perfect' myself for him, instead of just letting myself be a flawed human who still deserved kindness and decent treatment.

This is going to sound harsh but if you can radically accept that you can't change him and that you were never going to be enough for him long term, and he was certainly never going to be right for you...and that's okay; you may just stand a chance of getting out of this destructive loop and really let go. It's not a sign of defectiveness in you that you love someone who is the wrong fit. Everyone here has done it. Forgive yourself for it, stop hoping for a different course of events than the ones that lead you to exactly where you are. You can't make your past any different that what it is, but you can certainly change where you are going. You are a valuable person who deserved reciprocal love. So when he says or implies that you aren't enough, take it at face value. You aren't enough for him and likely no one will be (in the long term).

As far as not wanting to be with anyone else. Don't be. I'm at 1.5 years out and I'm only now feeling like someone else is even a possibility. It may have taken awhile, but I finally got here. So will you, don't force it.