My friend has a major crush on me. How do I tell him I'm not interested?

I'm a 13 year old girl, and I kind of think of this guy as my... sy gay friend, you could say. He's kind of feminine. (He's 14 by the way) It's really obvious that he likes me, and my friends joke about it all the time, but I find it really, really creepy that he likes me. I still want to be his friend, but I really don't want to have any kind of romantic affiliation with him. How do I get him to stop liking me?