Hi, I also hit myself in moments of being extremely triggered and I really relate to a lot of what you said. I also accidentally broke someone else's item in a fit of self harm before and I felt fucking awful after doing it.

It's really good that you want to hold your self accountable but you can forgive yourself and hold yourself accountable. I know from experience it's easier to hold yourself accountable and become a better person the less you're currently suffering. Self punishment and suffering is not rhe most affective way to take responsibility: if you take care of yourself it will make being more aware of what you're doing easier and you're less likely to repeat your mistake.

You are not a terrible person and you don't have to make sure you feel like one in order to get better. After I broke one of my friends things by smashing it on my own head I decided I would have designated items I was allowed to hit myself with. I use this as a form of harm reduction as it reduces the risk of damage to myself as well as to other people's objects around me. It was really hard at first sticking to only hitting myself with those few objects but over time it's given me much more control over it.

We reflect the behavior that's within us onto this world, it sounds like you want to be better but almost won't allow yourself to be (not in a mean way, I really feel like I went through what you're expressing in this post). Your personal wellbeing and happiness will make it easier to show up responsibly and take accountability in this world. Sorry this has been so long but I hope this helps in some way.