He's 20 im 15 but he has a girlfriend and he's my best friend's uncle?

he may seem like a decent guy but anything you two do, dear, is statutoryy seeing as he's over 4 years older then you and until your 18 that could get in the way. Maybe you should drop it and let destiny take its course. This really seems like a bad idea until you know exactly what you want from a relationship. It's going to be hard, but you should tell him if he really wants to be with you then he 1) wouldn't still be with his girlfriend and 2) he'll wait for you until you're 18. I hope I could help. You can look for your state in my source if you need some clarification on the law i metioned before.