Actually I think it usually is not possible to get back together with an ex. That's why they are called ex's. But then again, there is that tiny proportion of people that get back together with their ex's.
I think that what you should do is just go on with your life and stop contacting her or any of the like. Then see how she responds. If she comes back to you then that's all well and good. If not, she's not interested mate. Face it, you have to move on. I think many of us have been in the same situation as you before, as I have. Well I can't say I have totally moved on, but I'm trying to move on cos I know it will never be...
And depression sucks, but like I have said elsewhere don't let it get to you. Willpower mate. May the force be with you
But yeah like jslaughter said, how old are you?