Preferences change, all the time, plus... as in my own life, sometimes what you may normally be attracted to might change simply becuase you like more than just what a girl looks like. I tend to not pick a "type" or a look at all. but I tend to enjoy smaller women when looking around. That being said, the girl i like now is beautiful in spite of not being necessarily typical of what I tend to look at. Because I like HER for more than just that.

Could be a good thing for the OP. Maybe he does have preferences but has overlooked those to be with her and finds her attractive in more ways than what is skin deep.