I need a good advice

I met this guy a year ago. He is a volunteer and he lives with us. I just see him as another american before and don't really find him attractive. After a few months of living together in one house i began to notice that his pretty cool and we have things in common. We hang out a few times with his friends and my friends. One time we had a few drinks and with no intention we started making out. I really felt guilty about what happened cause we were supposed to be "brothers and sisters" so I talked to him about it and we both agreed that it was just the alcohol. But I felt something different and I think I'm already liking him. 3months ago he told our mom that he is dating this girl, after hearing that I really felt so hurt and just cant accept it. A month past and there was a party in our house, his friends, the girl his dating and my friends are there. Its funny cause he never introduced the girl to me and as if the girl just doesn't exist in that party. The girl went home early and we were still drinking. So he had alot to drink and out of the blue he was blabbering that he loves me and my friends were shocked of what he is saying. His friends just backed him up by saying that he loves me coz I'm his sister. I really didnt mind those things he was saying since he is a bit drunk. Then 2 weeks after that incident he invited me to a party in one of the bars here. We had too much to drink and both of us went home drunk at 4am. We still talked when we got home about nonsense things then while we were talking he grabbed my hand and began kissing me and he kept on saying he loves me. I was like OMG what are you doing ? but still he kept on kissing me and saying I love you. Well i also have feelings for him so i gave in. We ended up making out again. Then while we are making out he said he cant do it, he wanted to but he cant. Then I realized that its wrong too. Then he said to me that someday I will find my great guy but its just not him. He also said that he likes me but me and him just cant happen, that his longest relationships are like 8months and he has a hard time committing to anything. Well I'm thinking that I should be thankful that he is honest about it but you know that feeling of having to see him everyday is very painful. He will be living with us until November 2012. There are times that I just feel hurt when I see him go out with this girl and being with him everyday and pretending that I'm OK is even more difficult when I know that I'm not OK because I think I've already fallen in love with him.