So the quick version of this is that there is a guy I like that I think is gay but I'm not entirely sure and I was wondering how I could find out for sure that he's gay quickly and easily.
Get to know him better. Once you figure out he's gay, try and go for it. Quickly and easily?? You never know, he might be a really REALLY weirdl straight guy.
Quickest way is to just ask him straight out. What I do is see who they check out, guys or girls. It's not very reliable at first, but Overtime if they always check out guys then that'd be a sign for me.