I'm not sure if my best friend is straight

So I am confused by my best friend who has said is straight and has had several girlfriends in the past. We met about 5 years ago and instantly hit it off. 5 years later we live together, and things as great. Recently though I came out as bisexual to him and he took it well. The past few times we have gotten high though and even when we are not he makes comments like wanna fuck, or he will slap my ass, or make very long eye contact...it's got me confused.He hasn't had a girlfriend in over a year and I know he still likes women we comment on them often. I won't deny I am attracted to him, have been for awhile. I am just unsure what to do about it. Keeping in mind that we are very close friends, what should I do?