How to not worry about my girlfriend when she is out of town?

I have a problem of getting upset when my girlfriend when she goes out of town to visit her friends. The reason for that is because they all ways go to frat parties and it just makes me uncomfortable. She has never once gave me a reason to doubt her or not trust her but it seems that my sacredness from my last girlfriend cheating on me has taking a toll on this relationship. I look at it as if she not there then she cant have the chance to cheat. But that's not right to keep her confined, but I am afraid of losing her to someone else or scared that something will happen while she is there. What do I do to get over this fear and jealousy?