I'm a senior in college so maybe this will help...
Ok first of all, when a girl goes off to college she is usually getting a taste of freedom for the first time. Keep that in mind.
She is going to have more options dating-wise. She is no longer forced to date the local guys in the town she grew up in, or the local high school she went to in her hometown... And trust me if she is somewhat attractive dudes are gonna be hounding her. And they won't give a damn about her relationship back home with you. She will be fair game, and fresh-meat. Keep that in mind.
Freshmen girls are usually easier too...
I've seen a lot of quiet innocent girls come to my college campus and get turned out into party girls. By like the 3rd or 4th week of school.
People change when they go off to college, they get in a new circle of friends and they usually conform to act more like their friends...
Of course there is more sexual activity going on a college campus. Like I said people are usually getting freedom for the first time. They don't have to sneak around under their parent's roof. They can just go to their dorm room and turn the lights off. But not everyone is having sex. Its not like one of those American Pie movies or anything.
If I were you i'd let the girl go. She is gonna change and she will probably be getting some d i c k from some dude at college. If you do stay with her, if I were you i'd have girls on the side. But if you stay with this girl with the intention that both of you are gonna be faithful, YOU WILL GET YOUR FEELINGS HURT...