I'm not sure...I know I have trust issues due to being emotionally abused in the past, so that could play a factor in it.
Maybe it's cause I'm shy and not out-going at all to meet new people whereas if I know someone I'm more open to them.
And also there's no gays in my area, yes, I live in NYC, but my school is made up of straights besides 2 gays that I don't like, and I don't know any gays personally otherwise.
It could also be the fact that my friends think I'm just 'cute' and not seen as sexy or in a sexual partners-type way.