Every time I like a guy and I don't know if he likes me I try to make him like me but when I know he likes I get un intrested then if he has a girl friend I like him again is it wrong if I go after him I always want what I can't have

You're a teen girl hun. Every teen girl I have ever known including myself has wanted a guy who has a girl but when he is single he doesn't seem as interesting. So to your question nothing is wrong with you at all.