I am confused : am I bisexual?

Hey I ran across your site and wondered if you could help me. Iv been going through a bit of confusion, im not exactly certain of my sexuality. All my life, ive been attracted to boys. Ive even had the wonderful expierence of falling in love with one when I was 16. However, when I was 16 I also had my very first same-sex fantasy if you could call it that. It wasn’t very elaborate. I pictured myself kissing my best friend. No tongue or anything, just a peck on the lips. I had never expierenced anything like this before and I didn’t like it at all. It scared me and turned my stomach. I really began to think I was homosexual or something but I didn’t except it becasue of all the guys iv crushed on before. It just made no sense. Eventually it was cleared up but now I feel this way again. I tend to ruminate about certain subjects and this is one I just can’t seem to shake. Iv never had a crush on a girl but sometimes I feel like Im attracted to them, especially if they are tall and thin and close to my age. But the thought of actually being with a girl turns my stomach and scares me, even makes me want to cry. Ive only been with one guy in my life, and even though I didnt find him physically attractive or entertaining at the very least, he turned me on by the simpelest of gestures (holding hands and cuddling)
Another thing is that now I picture myself kissing everyone I see if they get close enough to my face, boy or girl. And in truth, Ive never even been kissed. So I wonder, Is what im feeling towards girls a true attraction or just something im making myself paranoid over?
~Alli