Dude just ask her straight up, tell her your understanding about the fact that she may be seeking satisfaction elsewhere then tell her how much you like her crotch and everything else about her and that if she wants to be with you then she needs to give it up more and be honest about the relationship, so that you know she likes you. I have known girls to lie and say they were hurting to hide the fact that they were sluts. They would say all the things that you would expect them to say to hide the fact that they are sluts. (I had proof to back up the fact that they were sluts.)
Especially if she has just gone off to college then for sure she may have turned into a superfreak. Imagine one of her guy friends coming up to you and saying the following.
"So... How do I taste?" ..............Yeah
Dont beat around the bush. Approach her with confidence, but dont be rude, dont act like theres no hope for a better relationship than the one you have.
Or yeah you gould go the van wilder route and say:
"I just want to make sure that our future children won't be tainted because mommy went slumming around one night while she was in college."