Man,I seriously had to learn this lesson not a week ago.
It's tough,especially if you have genuine feelings for the girl, but you gotta let it go. It's just a waste of your time to be the only one interested in being in a relationship. She obviously isn't and doesn't know what she wants. I'm the same age as you and understand what your going through but, you're young dude,you have so many relationships ahead of you. Relationships with girls who will care about you as much as you do about them.
So, I say cut your losses. Atleast she lives far away and you don't have to see her on a regular basis.