Does he like me? I'll answer yours! Easy 10?

So I'm 16 and so his he. His sister is my best friend and she's 15. I went to Florida with them about a month ago. When we were at an exhibit I was standing at a railing and he comes and stands a couple inches away then all of th sudden he moves closer to the point where his arm is right up against my arm and he doesn't move until his cousin came. Then at another museum we were at this exhibit and we were waiting for the rest of the family and it was just me and him. I noticed he started to follow me and when thunder went off in the exhibit it scared me So I jumped I looked over at me and he was smiling and kinda giggling. Then he stopped when his family came. Also every night he would come into my room and watch tv with me and we would talk. When we got back home I noticed that he always talks to me while looking in my eyes and smiling. Also when we went bowling and his sister was up he asked me about a Christmas present I got and wanted to show me something but I already saw it and he looked disappointed. When we went back to school that week I was walking in and noticed someone looking out the window, I looked away and looked back and it was him staring at me until I looked away a couple seconds later. Note: he only talks to me when we are pretty much alone, he'll glance at me a couple times, he doesn't give me any signs in school, and 2 weeks ago his cousin asked if he liked me but he said no, the staring out the window and bowling thing happened after that. Also when i came over on sat he didnt say one word to me and yesterday he came uo the stairs looked in his sisters room looked at his sister and said hi didnt even glance at me. So does he like me? Why does he only talk to me when were alone?