Don't listen to >>10 he is a cocksucker. You might as well go fuck a whore, because you always pay for putting on another dudes girlfriend.
You are right, nothing good will come out of it. If you want a lasting relationship, don't hook up with a girl who is passing away another guy by doing so. If you just want a good time, don't walk into a meatgrinder just because it said party on the door.
Smarten up.