Might my friend be gay?

I am gay male in college (I am about to graduate in a year) and I live with my best friend in an apartment who identifies as a straight male. He has never had any romantic relationships since he hasn't tried but he is pretty attractive and a really nice guy.

I also have never had any relationships since I am not out (except to him) and I haven't really tried (I have a lot of other problems in life that I need to deal with but that's an aside).

I have always thought of my best friend as simply a really good friend, maybe almost a brother, since I just assumed he was straight. That being said, I actually do think we would make a great couple since we have so much in common and have very similar principles, sexuality aside.

Now, I never entertained any of this since I always assumed that he straight but I am thinking that he might be gay, bisexual or somewhat curious. I say this since I accidentally stumbled upon his browsing history (shared computer / internet) a few times and sometimes (not very often), it contains homosexual male porn but more often than not it contains a lot fem-dom porn / BDSM (forced cum-eating, anal play, strap-on, denial etc.) and recently he was on an understanding sexuality blog.

I know none of the directly implies his sexuality (fem-dom / being submissive doesn't necessarily imply that one is bi, but I think it might mean he may be more open-minded or curious). I really want to see what I can do or ask to determine if he is bi-curious or bisexual indirectly.

I only say this since I would probably say that I would love to be in a relationship with him and I never cared until now since I always just assumed he was straight. What I am saying is that since I think we would be such a good couple (mutually), I don't want to miss out on simply because he wasn't out or comfortable with himself. I obviously can't make him come out (if he even is bi-curious), much less pursue any relationship, but I want to somehow indirectly try to make sure that I don't lose this opportunity.

I hope what I am asking makes sense.