Straight(?) Crush

Ok, so I have this friend. We will call him R. I have been friends with R since freshman year of high school; we are seniors now. Over the past year, we have gotten closer. I never had feelings for him, but all at once I started crushing on him hard. Like really hard. Anyway, there are a lot of people who think he might be gay, although no one knows for sure. R is very reserved, so it is hard for anyone to tell really. He never seems to like any girls.I need to find out if he is gay. I've had crushes like this before, but not this extreme. The only way I can move on from it is if I am 100% sure that he either isn't gay or isn't interested if he is.There's sort of a running joke in school that we are like a fake couple. It's all a joke, because no one knows either of us is gay and I don't even know if he is. It's totally fake. Nevertheless, we sometimes play into it just to be funny, so I am afraid that if I just tell him I'm gay he will be weirded out because he will know I like him. I don't want to say that unless I know he is gay and there is a shot, because I don't want to ruin our friendship.What do I do...