Im confused what do I do?

There is this dude i like alot. I knew he liked me and i know he still does. Ever since December when I met him Ive always felt so close to him. He had manners , we both liked rock music, and he was very respectful it was great! Until after a few months;He started ignoring me, started acting cocky , and now will even piss me off just for the hell of it. (he smiles from ear to ear when I react) I dont know whats the matter. Ive done nothing to him to make him treat me like this. All of a sudden he started saying I was weird and he's heard stuff about me!He should be the l;ast person to call any one weird.( i caught him talking to himself numerous times ).And to make things worse his sister and her friends dont like me at all.While his friends dont mind and half of them i know myself.I tried talking to his sister about it but she claims she knows nothing (Lies!) Hes always looking at me and sometimes i swear i can see love in his eyes. What can i do to make him see im more then what people say about me and get the guy i love back.And maybe how to just get along with his sister. Please help!He's 17 Im 16.