I totally get what you mean, my boyfriend and I are going through the exact same thing. I'm already at uni and he's going this year. We love each other to bits but at the same time, we've been together so long we both sometimes feel the desire to break up, its playing havoc with us at the moment because we don't want to break up, we may never find something this good again, but we can't carry on the way we are.
I'd say definitely talk about it, and you will have to break up with her, because its unfair for both of you in the long run to be in a relationship that you're not fully committed to. It's going to hurt her whichever way you do it, its a sad fact of the end of a relationship, but you have to learn not to blame yourself because you can't change the way you feel.
Good luck x x x