My boyfriend got mad at me for believing his sister about his behavior

My boyfriend and I have had a very toxic relationship. My therapist highly suspects he has borderline. He has blown up on minor occurrences and will propel himself into a hate fueled rampage where he’ll insult me and make insults about other people in my family or m friends. He’ll often then turn it around and say that I’m the problem if I am critical to him about petty things (like parking in two parking spots) and how I ruin every time and embarrass him. For example, when I refused to sit in the same area with his mom who verbally assaulted me and used slurs to demean me. He has had instances where he has gone off on people and has been extremely reactive over petty things. As a result , I recently have not been very affectionate and have expressed concerns that I can’t really be with him unless he seeks therapy. He has used that to try to frame me as treating him horribly. He will then love bomb me after he goes off about these things.

There was an incident where an escalation broke out with his severely mentally ill sister and he had to restrain her to prevent her from hurting her family. When he did this, his other sister called me to tell me that she was worried he hurt her, tho she wasn’t there. She then said that he had tried to attack her before and pulled a knife on her once.

I of course was really alarmed and told him I can’t be around him. Well it turns out , that sister is extremely dramatic and will distort things when she’s under stress. She called me back saying that my bf was actually helping in the current situation and she misread things without addressing the claims she made about the knife, acting like she didn’t say that.

I apologized to him for believing her and that I was honestly worried about dealing with a serial killer or something. He has since lashed out at me saying “you’re so dumb for believing my sister” and how insulting it was for me to think he was capable of being violent like that. I know I shouldn’t have jumped to conclusions but honestly this incident wrapped in with everything else has been extremely overwhelming and I do get scared regarding my bf due to his extreme reactions