Your not alone my friend =].
I was in your boat... there was a guy who was into me... owww wow I couldn't believe it when there where a lot of slimmer,cooler,prittier girls more than me... and I used to say he has that girl who wants him and she's so good looking why is he holding on to me?
Now I settled with it and I am seeing myself pretty =]
It's still the same looks I used to have... I just needed someone to tell me that I have nothing less than anybody else and neither you have ;).
So instead of stay there wondering why she chose you get the positive(it has no negative side anyway)and believe in yourself no matter how many people call you ugly... or useless or stupid stuff some people used to call me... you'll get used to it and say ohh they're just jealous instead of going home crying so get yourself esteem good and enjoy this life...