how to prevent from falling inlove with your bestfriend?

You don't have to prevent it, I don't see anything wrong if you express it, how would you find out if this girl might have the same feeling as you do? I mean if you are still young, maybe you would agree on certain terms that you could retain the friendship and respect for each other when you confide this matter to her, if your intentions are good why bother deprive it ? Just my thought.