How do I make things better?

Last night I apologized to my boyfriend. Lately I’ve been mean to him and haven’t been showing him a lot of affection. I have borderline personality disorder. I know a lot of you don’t know what that means but one of the main symptoms is “splitting”. Basically going from extreme idealization to extreme devaluation of my partner all the time. No in between. I’m trying to work on it but he doesn’t understand and he gets very hurt. When I apologized last night he started crying and I comforted him before going to bed. Today he’s been very mad at me. Everything I do that he doesn’t like, even things that don’t affect him, he gets mad. I don’t know why he’s acting this way or how I can help the situation. I wonder if you guys have any advice?