I have been dating this guy for almost a year come August. He slept with 2 of my sister prior to me and now we are together. But the problem now is that he still deals with 1 of my sisters and I don't get along with her. My sister is now homeless and I have been allowing her to stay he sort of. But since I don't speak to her and the things she has said to me we argue almost everyday. I am in love with this guy but it seems that she is putting a damper on the relationship. What should I do?