Hi Larmoyant
At the end of my relationship I was angry with him. I’d had enough of the cruelty and soul destroying push/pull so when he wanted to talk, then kept sabotaging my efforts I reacted in anger. I couldn’t take it anymore and this saved me. It gave me strength to get away.
I guess the reaction of anger gave you strength? If so, then I can relate. I used it to fuel my desire to cut the relationship. I generally don't recall many angry times with my non-pwBPD partners, so it was quite difficult and "new" for me to use anger in this way for this sort of relationship.
I wish I could stay angry, but I can’t. My feelings towards him change.
I believe I can relate to this. I asked one of the admins this year about this want/un-want of anger. I can't give you a perfect answer to this as I'm not a T or P. But this was good enough for me.
Ask, "Why was I angry?" For me I saw that anger was to be a barrier against other BPs. "No way in hell I wanna go near a BP again after what that * did". So the anger functioned to help me with this. So I really wanted to remember the suffering, anguish, and pain for this reason. Gosh no more BPs please.
But carrying that anger is stressful and it can also falsely push you from healthy others.
Yet, I also felt compassion. I could quite clearly see many reasons why she's as bunged and knotted as she was/is. I also saw these things in my bio family. It made sense. So: understanding and compassion. Yes, it is heart breakingly sad. It becomes even sadder when we amp up how we can
feel the pain as
their pain amps itself up. More pain can cause more caretaker reactions.
I don't know if this is consistent what what you're feeling, so perhaps it's best simply to investigate why you want the anger. Then perhaps why you feel the compassion. But I do think you will get a
lot from thoughtfully questioning this part you wrote:
I sometimes feel sorry for him because I’ve seen the ‘abandoned child’ in him, it’s heart breakingly sad, and makes me want to help him, but then again I fear him.
This tells me you have an opportunity to perform acceptance of the fact of
his abandoned child. Recall that acceptance is allowing something without feeling that you necessarily want to get involved. Explore doing that and question
why you have this compulsion to help him. You didn't mention it's a "compulsion", but for me it was. I encourage you to figure out your why. It could be a real gem in your healing.
At the same time, I was doing quite a lot of work on forgiveness, so I encourage you to try and look into that link Naughty Nibbler suggested.

I hope this all helps with your odd hodgepodge of feelings.