I want to know if I’m being unreasonable and this is a symptom of my BPD or if i’m justified in feeling this way. 

There’s this girl that my boyfriend (and fp) used to be friends with. A couple years ago before we had met we were at a party and she keyed everyone’s car there, including mine, for no particular reason. At least not one that I ever found out. She didn’t even know so much as my name at the time either. Shortly after, my boyfriend and I started talking and since he was friends with her there were a few times in which we all hung out together. She blatantly lied to my face and told me she had never done it and my boyfriend, who had watched it happen never said anything different. I suspected it was her the whole time but it wasn’t officially confirmed until about a month or so later. Basically after that I told my boyfriend that he had to cut ties off with her because I thought it was extremely disrespectful for him to keep being friends with her knowing what she’d done and the cost of the damage to my car. He was fine with it until today. I found out that he had added her again on snapchat. I, of course, completely lost my temper. He does have a side business in which he sells stuff and he claims that that’s the only reason he added her. But I still think it’s extremely disrespectful and without regard to my feelings, knowing what she did to me. I told him he had to delete and block her now and he exploded on me saying that he was gonna leave and break up with me because he’s tired of my complaining and my urge to  self harm any time i’m triggered. He refuses to delete her and I feel like he doesn’t care about my feelings about it. Just to add, he is friends with other girls for his side business and I deal with it but I felt that he crossed the line here. Do you guys think i am justified in feeling this way?