Why does my girlfriends older brother hate me?

he seriously does not like me I have tried everything to get him to like me but he refuses. hes tried to hit me with his car told his friends things about me so when I walk past them they are laughing. at me. he is always giving me this cold look when I walk past him. me and his sister went to a carnival and I invited him when we were at the carnival he wouldn't let me go on a ride with her he kept cutting me in line and I got her some food and he knocked it out of my hand and told her that he would buy her anything she wanted. I won a inflatable kitten because she likes that and he stabbed it with a fork. so I got pisted and got in his face and told him he is acting like a ***** and that he needs to knock it off because I am going to date his sister. he told me that he hates me and that his sister is the only thing that he has left as a real family ever since their parents died and that I was not going to take that away from him. so I asked him if he ever heard of sharing and he said that he doesn't believe in sharing so I just walked off.