Lemme lay down the foundation for you.
You're at school, minding your own business, feeling like crap that your last relationship ended badly. Suddenly, you see the perfect girl sitting across the room. You introduce yourself. Get to know her. It turns out she's an exchange student from across the country. You hit it off. And suddenly you realize... she'd be the perfect rebound.
You start dating. Your friends point out her flaws, but you don't mind. It'll all be over soon enough, right? But, as time goes by, you start to realize that you don't want this to end. So what now?
The end of the semester comes. You think this might be an okay out, and make it easier for you not to hurt anyone's feelings. She flies back to visit. You realize now that you don't feel the same way about her anymore.
What happens next?
Well, you don't want to be an asshole. You don't want to hurt her feelings. These are your reasons for not breaking up with her. But let me remind you:
Leading her on? That would make you an asshole. And it would hurt her feelings.
This is a time when you need to rip the Band-Aid off quick. Be nice about it, obviously, but tell her:
"I realized during your visit that I don't feel the same way anymore. It's nothing you did or I did, it's just different. Plus, the distance is making it much more difficult than I thought it would. I could never lead you on or string you along, so I think the easiest thing for us to do would be to part now."
If you still want her friendship, that's your choice and hers. But this whole conversation? Not so much a choice as a necessity.