Insert cliched title, eg "Confused"

[MN1]

I haven't been in a relationship since I was about 15, and even then, that wasn't real... and it was with a girl. I've been into guys as long as I can remember but have never acted on it until now. I've always avoided getting close to anyone because I like my own space. Just a few months ago I had a shot at something good with an amazing girl and I left it because I felt scared about letting someone be part of my life. Now all of a sudden I find myself facing the prospect of a relationhsip with a guy and it's making me feel awful. I can't even explain why because it's something I've been quietly hoping for for quite a while now. He's the first guy I've ever even kissed. He's nice and all but when I'm with him I feel a total 50:50 split of contentment and disgust with myself. That sounds really horrible but it's just the way I feel. He seems really keen but now I'm finding myself making up excuses to avoid spending time together. The last night he came over I found myself wishing that he was her. I'm so confused. I was so sure about my sexuality but now I'm having doubts again. Is it possible that my being into guys is nothing more than a fantasy that I had to try out...? Or is this what they'd refer to as phase?