Mad at myself for losing my virginity

I lost my virginity to this guy who I'd only been with for like a week. (He wasn't a virgin at the time). I didn't even like him, nor did I find him physically attractive. I don't understand why the hell I did it. Even though it happened 2 years ago when I was 15, I still haven't been able to forgive myself. I mean how could I have let someone I barely knew/didn't even like be the first one to have sex with me or even see me fully naked for that matter. I used to always imagine losing my virginity to be special. Even though it happened so long ago, I can't get over it and it's eating me alive. Please, please give advice.