I was actually about to post something similar in response to your earlier comment about people assuming you were a heterosexual female. (Er.. I'm not stalking you in here, I promise?
).
People pretty much always assume that I am a heterosexual female, too. But.. I'm bisexual.
I also have a close male friend who is gay, but also does not appear so. People think that we're a couple all of the time. Yet people never assumed I was dating any female (whether we were or not).
I'll admit this story hits somewhat close to home for me. It makes me wonder how many people would not have tipped me (or discriminated against me in other ways) if my sexual orientation was more obvious.