My GF is acting So dumb!!!!?

She basically doesnt have any social skills 0%. Thats probably why she doesnt have any girlfriends, they are all guys. We cannot go to bars or clubs coz she's still 20, am 25. We were invited to this party at this girl'shouse along w her brother and his GF. The problem is, the girl who is hosting the party knows a guy, a friend and a naighbour of hers, who was my GF's friend, and I suspect that they had a short affair, the thing is, is that I had an argument w this guy before, and we almost fought, he basically was at my GF's apartment after I left one day, and I went back I forgot something and I found out that he was there, and although he was so scared when he saw me, I fainted because I couldnt stand him being there. I dont know if they did anything, and the worst part is the fact that my GF stood by his side. The thing is, my girlfriend is so dumb that she kept saying, oh I wanna smoke with that guy when we go to the party and she kept asking that girl about him right in front of me!!!!!WTF, they left an hour ago and I told them that I will catch up w them, but how am i gonna go there, I am so embarressed to go, I am embaressed to show him my face, but she put me in this situation, and the thing is if I complain I am the insecure guy, if I yell I am the jelouse guy, if I keep quite she will do it again. WHAT THE FU&% AM I SUPPOSED TO DO NOW< GO OR NOT?