I think I'm in love with a 17-year old girl even though I'm 25
Why do you think you're in love with this young girl?
I think about having sex with her all the time.
Fantasies about being with underage girls are not to be tolerated. Find someone your own age and have a mature, loving relationship.
It doesn't matter. I want to protect her as a person.
It doesn't sound like you want to protect her. The first thing you thought about was sex and either way you are still too old for her.