Are you a jerk? No, not at all.
I don't think you've fallin in love with this new girl though. Hardcore lust, sure... I think a part of it is the fact that she's a cute, nice girl. And she's there. Your girlfriend (ex, whatever) might be cute and nice and all that as well. Yet she's 11 hours away.
My advice? Break if off for good with your girlfriend. Long distance relationships during college are so rough. Take the time to get to know this new girl, and don't rush into anything. It sounds as if you've got some sort of connection there, so see where it goes.
I think your girlfriend would be best served breaking up as well. She sounds pretty miserable. Sure, she'll be hurting for awhile but long term she'll be okay. And who knows, maybe when summer rolls around and you're both in the same area again things might heat up between the two of you.
My $0.02.... Good luck
Oh... the whole dating other people thing... I've never seen that work out well. Somebody will get hurt. Best to just make a clean break.