How do I get back to normal after relationships.?

I've only had one serous relationship in my life and after it, I feel into a very sad, almost depressed mood for awhile. I am currently in college and was seeing a seemingly "good" girl for over a month. I was completely happy single before her, but I still ended up being with her for awhile. She was very pushy and the aggressor to be with me and make me only with her. All of a sudden she became distant and basically stopped everything. Now I still keep in touch with her, but this new imposed stress has been building and seriously affecting me. I don't want to become what I was like last time. Does anyone have any advice on how to get back to being happy. Also just going out and hooking up with girls doesn't help and is not me whatsoever. Thanks for your suggestions.