To me, the big thing here is that he's opening up a bit and talking to you about it. Actually voicing his feelings is difficult (I would venture good feelings as well as bad).
Maybe instead of thinking "I don't want to save this M" you change gears to "I want to successfully co-parent." Maybe that is a line of discussion you can have with H to make the current sitch a little bit better. I know thinking about my kids really helped me with that. For the sons, how we treat our W is how they think they are supposed to treat theirs. When they see us disrespect each other, they believe that it's ok to behave that way.
Honestly, every time that he acts out at you, it's him showing that he's hurt. It sounds like you may be at a point where you can address this with him....acknowledge his hurt but maybe let him know he can simply tell you, "I hurt" instead of acting out. Show him compassion without piling guilt on yourself.
With that said, I have to ask, have you forgiven yourself?
