What do I do about his relationship. Do I end it?

I am the same age as you guys and have been put in her shoes quite a bit. She probably feels like you are too clingy and didn't know she meant THAT much to you, she's not trying to hurt you but more like trying to move on with her life so to speak. It might not be over for good so be optimistic but don't try to be around her all the time. Chances are they will break up and she will remember what you said and try to patch things up. Good luck, hope that helped! :)