Abusive or mentally ill?

I know this is long but i really need help here, and i dont have any friends. So 2 years ago i met this guy, we fell in love and have been together ever since. 3 months into the relationship we would get into little arguments amd he wpuld punch walls and call me a bitch, months later he started calling me worse names and began threatening me saying that if i ever leave him he'll hurt me. I always thought i deserved it because sometimes i call him names to, but i never punched walls or hit him. As time went by our fights got worse, if i wanted to walk away he wouldnt let me by pulling me back or standing in my way, one time he got so angry at me that he grabbed me by the collar of my jacket and literally flipped me onto my back on the ground. (Iam quite small and hes large) but right after, he started crying and saying how he was so sorry for doing that and how he lost control, and begged me to stay, of course i stayed since i was scared he would hurt me if i tried to leave and also felt bad for him. When we were good we were extremely good when we were bad we were extremely bad, no in between, after thr day he flipped me he said he felt so bad that he went out the next day and got my name tattooed on his rib cage. But as time progressed he became more aggressive. Fast forward a year later him and i got into an argument and he ended up putting his hands around my neck and straddled me so i wouldnt escape. I called the police that day. He was sentenced to therapy. Thats it. Anyways, i continued to talk to him after that because i felt bad and he continued threatening me after that. Also, he was my onky friend at the time because in the process of dating him i had isolated myself from all my friends that i lost them all. Anyways, he went to a psychiatrist and was diagnosed with borderline personality disorder. Just when he seems to be doing better in therapy, he goes back to his ways if he gets mad at me and starts threatening me again and calling me names. I know its stupid that i still love him, idk why, maybe its the daddy issues. But anyways, i cant tell whether hes just abusive or if its his disorder that makes him like this, i feel bad about leaving him if its his disorder because he has been ther for me thru my anxiety and depression, why cant i seem to pull myself together to be there for him for his disorder? Will he ever change? I dont know what to do. Im slowly falling out of love with him. Very slowly.i dont need negative comments, you may think im dumb, but dont point it out, i feel bad enough, i just need advice.