I think this is a symptom of a personality disorder but I'm not sure which one. Borderline, maybe?

When I feel threatened or jealous I become very mean and abusive to my boyfriend.

I don't have a boyfriend now, but I have been chatting with a guy for over a year and I have feelings for him. I am jealous because I saw he was flirting with another girl (online), even though this was years ago. Like 3 or 4 years ago. But it still bothers me. I think he must have liked her more or he still likes her and I'm just the one he talks to in the meantime, because he can't have the one he wants. (She ignored him).

I don't know if any of that is true, but that's how I feel. So I became very mean and abusive to him and told him not to talk to me anymore, etc. I can't control myself. I know I'm being irrational, but I feel so hurt and jealous and I can't stand thinking of him being attracted to someone else. Even if it was years ago.

I know I sound like an awful and insecure person. I've ruined all of my past relationships because of this.