What do you think?

My best friend over the internet, he's a male, fan of yaoi, he uses a lot of all sort of gay jokes, his actions are truly confusing. At some point he always comes out as straight male, still often he acts more like someone who wouldn't mind going out with dude. I never asked directly what sexuality he is, however as we talk again it more seems he's straight.

The issue is I became interested, I don't want to be too obvious by asking straight away if he would mind going out with dude since he knows I'm bi and I am afraid he's not so dumb to not put the hints together into one solid piece. Sadly he treats everything I say as joke, so far I didn't mind but I feel like if I try to have serious talk with him, he'll back away or find out.