What the hell...

Lately I've been jealous of my best friends boyfriend. I wanna punch him in his face when he's rude to her, I wanna punch him when he's too nice, I wanna punch him when he touches her, I just want him gone. Lately I've been catching feelings for her and I don't know what to do. Somedays I feel like she has some for me but I'm not sure. Shell kiss me, touch me, we've even had sex, and she told me she doesn't think she wants to be with him anymore... what do I do?