If he is firmly in the closet, maybe you'll even marry and have some kids (God knows, there's plenty of relationships and marriages out there like this now!)

But eventually nature will take over and he'll realize that he really prefers men to women and then you'll be stuck dealing with things.

A leopard can't change its spots.

Better engage in some introspection and think about what it is about him that you're attracted to (he treats you better than most other guys have, he's funny, kind, etc.), and what it is about him that makes you think he's in the closet.
If he is gay but still in the closet, even if you ask him he won't admit it -- so not sure if it would help having that conversation with him.

Sounds like you've got a lot of soul searching to do...
Good luck!

"Most plain girls are virtuous because of the scarcity of opportunity to be otherwise."
-- Maya Angelou