Before I was officially diagnosed and early on in the med changes until we found out what meds worked for me I was breaking up with my wife (gf at the time). I spent a lot of the first few years in and out of a manic state (which was actually the reason my wife said get help or I leave).

I broke up with her because I thought she was holding me back. I broke up with her because she deserved better. I broke up with her because at the moment I was really pissed off at her and couldn't see the forest from the trees. However, every time I became stable again I went back to her and we moved on (I never cheated on her when we were "separated" though). Once we knew what was going on she'd often ignored my "I'm breaking up with you" and would tell me that I didn't mean it and it was just the bipolar talking and we'd talk when I calmed down.

I dunno if this is what your bf is experiencing but I just wanted to let you know that it could possibly be due to his mood. But it could also be that he's done with the relationship. I do wish you the best.