I think my room mate is gay but I don't know how to ask him?

Why does it matter? Are you gay?

Just trying to find out more.

What you say "roommate" are of the opposite sex and have a relationship with him.

Or you the same sex and find him attractive ?

At the end of the day, you just ask him

Are you afraid he's hitting on you? Are you trying to figure out if you should hit on him? Which side of this are you coming from? And what makes you think he might be gay?

Why do you think he is gay? Are there any distinguishing characteristics displayed by gay people?

Is there a reason to know? Would it affect your relationship to find out he is Bi?

A person's sexuality should play no part in living arrangements unless the person is hitting on you, you want to hit on them, is being blatant about it to the point of indecency or being inconsiderate (bringing home a new conquest every night, making sexual noises so loud a freight train at a railroad crossing seems quiet, etc.), or you are trying to fix him/her up on a blind-date.

Why do you need to know?

Why does it matter if he is gay?

Does he have the right to know the details of your sexual practices?

Ask him if he could pick any one person in the world to spend eternity on an island with, to be his mate for life, who would he pick?

What does his sexuality have to do with you?