I think there are situations when there is more temptation for a guy or a girl to cheat and nights out happens to be one of them.
However, when someone cheats, it might not be in the situation you might expect. Like you said, you can't know what may happen in the future but if you know yourself then she should trust you.
Honesty and trust are the key foundations in a relationship and whilst every girl can have moments when she feels a little insecure, for your girlfriend to be worried about 'all hell' breaking loose seems a bit of an overreaction at this point.
Expansion in your social life does not mean you will cheat, nor does you staying in imply that you are less likely to cheat. I know plenty of guys at university who are in LDR or with their partner and are completely faithful - at least I can say this for the couples I am close to.
Its ok for her to be concerned but seems like she is worrying too much especially when you have given her nothing to worry/be concerned about.