Do you think my friend is gay but doesn't realize he is or is closeted?

If your friend is cool with you being gay and wants to spend the holiday with you, then of course there's a chance that he's gay too. It may be that your mutual "gaydar" is what attracted you to each other as friends in the first place. I'd talk to him about it, without coming on to him. (I definitely get the impression that you're attracted to him--am I wrong?) If he is gay, you go from there. And if he's not, it's very cool to have a straight friend that you can be yourself around and not have to worry about what he "really thinks" and all that nonsense. Good luck, and have a great holiday.