It's killing me inside - got any good advice?

Hi guys!First, I just want to say that this is my first time ever writing down my feelings thoroughly like this -- but I really feel like I need to get it out and off my chest.As an intro about myself, I'm a very professional and courteous 23 year old gay male living in Phoenix. A few years ago I started college and ran into this guy named Steve. Steve was in a fraternity on campus and I was interested in rushing Greek. I got to know Steve really well and eventually Steve and I were hooking up every few days (we are also now fraternity brothers). We were doing this for a few months until I noticed that something was up because he was starting to act weird towards me. I eventually found out through his phone that he in fact had a boyfriend - and he never bothered to tell me about him. We ended up getting into a huge argument and we eventually stopped being friends for a few months. We talked it over, and figured out that we could both move past it -- but boy, was I wrong. Long story short, I'm now living with him and his boyfriend (who he used me to cheat on him with), as well as another roommate (so there are 4 of us total)..... I don't know why I did this to myself. Every day, I'm consistently in a daze about how I am supposed to feel about the whole ordeal, and I constantly question myself on why I allowed his boyfriend and him to move in with me. Every day I am reminded that they are together and that I will never be apart of that equation. It kills me inside. I still have plenty of feelings for him, but he likes to walk all over me and he knows that I don't like it. For example, Steve always hangs on his boyfriend and they are constantly hugging and kissing in front of me, etc. At what point can I confront them and say enough is enough?! Another example - the other night we were out barhopping for my other roommate's birthday; Steve was talking to me in the hotel room we were staying in that night, and he kept making advances towards me even though his boyfriend was right there infront of me! He would come and sit really close on the bed next to me and try to talk to me and rub his leg on me.... I hated it.Anyways, it's gotten so bad recently. Now when I come home I go straight into my room and often sit in there doing things (such as blogging, posting here, watching movies) just by myself - I hate seeing them together, and I hate that Steve acts like there is nothing wrong. He knows what he is doing to me and it's not fair...Any advice?