Questioning

I'm a 27-year-old woman. For many years I've had fleeting thoughts that I might not be completely straight. Mostly this has just been in passing. I've had many relationships with men where I just wasn't attracted to them but I figured I just hadn't met the right one. I know I've been attracted to at least one man.
Recently though this questioning has become a lot more serious and it's tearing me apart. It's not just that I'm bi or a lesbian and afraid of coming out, the problem is that I just don't know.
I'd give anything right now for a bit of certainty. I want to be straight because it's easier but I mostly want to know. I am crying all the time and hating myself and I'm too confused for words.
How am I supposed to know? Does having failed relationships with men make me queer? Surely not. Am I attracted to women? How do I know what it really means to be attracted to someone? I really don't want to be someone who toys with other people in the interests of “experimentation”. I don't want this to be something I'm doing to myself because of other frustrations. I don't want to be embarrassed by going through this and determining at the end that I really am straight. If I am queer I don't want to come out. Mostly I just want to stop crying all the time.
I haven't told my straight friends, at least not seriously. I've said “I think I might be a little queer” before but although I always thought it might be true, I never really believed it. My queer friends have been very supportive. The common comment they have is that it reminds them of what they went through. They keep telling me that it seems unlikely for me to be this anguished about something if there isn't anything to it. I will feel like an idiot though if I figure out that I'm straight and went through this for nothing. My worst fear is that I won't figure out anything. I really have no idea of what my orientation is and no way to figure it out. I won't be relaxed enough to seriously consider dating women until I already know the answer to this question.

I don't have any neat conclusion to this story. I just thought that someone might relate to the feeling of having your life consumed in uncertainty and feel a little less alone.
Anonymous, Ontario