Thank you so much for all the advice everyone! He came home about 20 minutes after I posted this and I did manage not to ambush him. We talked for awhile about my problems with him and hanging out with this other girl. And, to his credit, he agreed with me. He hadn't thought how it would affect me bit as soon as I brought it up this time he listened to me completely and we worked it out. Even if we hadn't I would still be here. It wouldn't be very committed of me to just leave him because of that. If this keeps going, or if he does something again and I find out, then that's a different story. But for now, I think I'm going to concentrate on making us work. If we fall apart, if we start having really bad issues, it'll just add on to everything I already have going on in my life, mentally as well as other issues. Thank you all for the advice, and if this happens again, now I have all your words to fall back on and think about. Wish me luck!