I understand what others are saying here. However I think this might be a different thing from plain self hatred.
From your post, I would say this is a fetish that you can't quite understand yet. You mentioned that it isn't *always* sexual, which would mean that sometimes it is, correct? Deep down it might be a sexual thing even if you don't get aroused by it all the time.
Are you a submissive? Are you sexually submissive or find pleasure in it? Even if you've never done this, do you think you would enjoy it?
I'm sorry for all the questions. I've met people with all kinds of fetishes and have been involved in the BDSM community for some years now, not as a practicer (although I have my kinks too), but because the psychological side of it thrills me and I think it's absolutely intriguing.
My advice is: seek therapy. Talk to someone about it and try to explore all the possibilities as to why you like being hit. Exploring all the possibilities means going through your whole life. Have you been hit by family members, or close people? Have you ever felt this before with ex partners? These are the kind of questions I would explore.
Having someone you can relate to might also help, so I'd advise you to look this up on Google too (I always do and it always helps).
Regarding your relationship, I don't think breaking up is a solution and it will only probably just make you feel worse. You guys obviously love each other, and although your boyfriend *is* hitting you, I believe he's just doing it to please you, no matter how bad it feels to him. I think he would be happy to help you understand this with you, and he could probably use some kind of help too, in order to understand better and deal with it.
Good luck!