It's a sort of que sera sera situation. If she's the type that will cheat, then she might, but if she isn't (if you know her well enough you can gauge this, although they also say you never truly know anyone...hmm...) anyways, if you can talk to her, then tell her you're feeling a bit insecure, and you'll have to trust her if you want to stay together. I will say though, although a lot of people with a partner at uni envisage wild parties and being wasted - which is true, but I know 3 girls here who go out and have a wicked time, but come home to bed on their own, with a photo of their boyfriend there on the bedside to remind her of him. If she loves you, I'm sure she won't.