Love, Relationship, and Dating Advice Online

I need help dealing with my 3 1/2 year relationship ending. I love my ex boyfriend, Brandon very much. He transferred to a state university and the same day that he moved into his apartment he decided that it was time to end our relationship. He said it was too stressful (which it really can be). I’m devastated because he usual speaks highly of our relationship and tells me that we will get married when we are finished with college. Now just like a flip of a switch he wants out and wants to meet other people and "enjoy his life". I honestly didn’t see this coming and didn’t realize I was preventing him in any way from enjoying life. I really wanted to be with him for the rest of my life, now I don’t have him at all. I’m extremely depressed, constantly crying whenever I’m not occupying myself. I’ve been out with my friends and have met new people and school started but its still not enough. I feel like a mental case that needs a psychiatrist before I do something harmful to myself. I know may others deal with long relationships ending, if you have any positive advise I would really like to hear it.