OP just has to simply ask "straight" friend if he is gay. He's probably discovering himself, and he's probably not ready to start telling people he is bi/gay or not. From what OP tells us (which may be extremely exaggerated), I think crush has a pretty good chance of turning out gay, but it might just be bromance that is going on.
If he isn't gay, then that is that, you should just ignore your attraction because you can't make someone gay. Sure, if he says he is straight, maybe he is just so far into the closet his ass is in Narnia, but you can't know unless he tells you.