Best Friends Question?

So, I have this best friend named---lets call him *John because he might be reading this---and I have this kinda small crush on him. Too bad he's already going on with a girl---lets call her *Betty---whose a senior. (FYI: John and I are juniors). So anyway, how do I tell John that I have a crush on him and that Betty might not be the right girl on him. (FYI again: John and I are FWB {friends with benefits}) Help!