I don't know what to do =(?

I'm 17 living with my sister and her boyfriend.it was either move in with them and get my own room or stay at my moms in a nasty (disgusting) old basement.I have always had problems with my sisters boyfriend and have tried nearly everything to like him but he disgusts me in every single way and he gets on my nerves by saying stupid little things to me to tick me off and he knows what he is doing but he doesn't care. Is he trying to get rid of me? or is he just a complete ***? Not only that but he gropes my sister rite in frost of me all the time making me leave the room and then they always ask why i am in my room all the time.I caught them the other day having at 4pm in the afternoon with there door wide open so i confronted them later on and all they did was laugh,kissed and then he said "its my house i can do what i want,i pay the bills (hardly)" Am i crazy or is this not rite? Then he has the nerve to ask and borrow things from me to later on find out he never gives anything back to me,i mean when or if i borrow things i give it back when i am done not throw it on the floor to have me walk across upon it later to find out that its either ruined or broken! And then when everyone (happened more than once) is around he asks me rite in front of EVERYONE why do i hate him so much,i never said anything to him about hating him or anything else,i usually just ignore him if he does something to tick me off so if he is asking me that he must know he is getting to me and trying to turn it around back at me making me look like the bad person! And then on top of everything when i or if even i walk into the same room as him (he is so lazy) he constantly asks me to get things for him like i am his slave or something. Now you understand why i hate him so much.I know it prolly ain't the best thing for me to be living there but i just cannot go back to that basement (you wouldn't even know).