Ok.. I'm gay and I like this guy and I need help. Please help me.?

Im a freshman at an all boys school.. And I just got to know this guy in my class tut I really like. But I don't know if he likes me back or he's gay. We talk sometimes at school about regular stuff and one time at lunch he called me sexy... He also has a friend that he's know since grade school ( I think his friend is gay to ) but I wanna know how I can tell If he's gay with out asking him.. How he can know I'm gay without me telling him.. How can I know if he likes me without asking him.... How can he know I like him without telling him.. And how do I ask him out? Pleassse help me :( I really like him.