My ex and my jelousy over her being with old my best friend.

My ex left me because she had feeling for my old best friend who went I started dating we threw a fit about it started talking crap about me and telling ppl he loved her. She broke up with me and after the fact said it was because of him but then when they tried to get together it didn't work out. We all frequent the same bar music venue and ever time I see him it pisses me off. He apparently was absusive to her and he like litteraly started at her and glares meanwhile her and I have a positive realationship but I get EXTREMELY jelous and it comes out as anger. I afraid she will go back to him and if she just treats me as a friend like why doesn't she not go back to me. We are not involved sexually at all right now but I'd like to be and she I think is more attracted to this gus for some reason and it's not that he's more attractive at all. I now have no self worth and have intense anger and jelousy issues. I don't know what to do about it. In afraid it will ruin my life.