My gf got SA, I want to get vengeance

For context, two years ago my gf got SA by this guy, I’ve been with her since one year now. It is very hard for us since she has PTSD and we can’t do many things, but I’ve always been here for her and always be. She kept this for her btw, no police involved, she doesn’t feel to do it. I really feel powerless since I feel like I can’t do nothing. I’ve always been a peaceful guy but seeying this man just walking and being happy gets me extremely angry. From what I know, this guy is a “popular” one, he has many friends posting about street life and things like that, I am alone. Tonight there is going to be a party and I know we both are going to be there. I know I’m about to do something stupid, please give me some advices before I fuck my life up.