How do I comfort my girlfriend if she's crying?

Well it depends on what the problem is with the girl. 1st thing I'd say is like, that your here for her and that she can tell you anything. Sometimes you should probably ask whats wrong. If she says she doesn't want to talk about it then tell her, its gonna be a growing problem if she doesn't discuss the matter at hand. If the girl is giving u short answers like "i guess, sure, idk, etc." That will probably cause problems for you. You might not know what to say after that. Just say that you don't like it when shes sad like this, and that it makes u sad. Tell her try not to be sad for too long, or else it would become a growing habit. Which you probably wouldn't like. Also tell her that you don't want to lose her for who she isn't. (: that's all i can think of. peace ^^*