You must first cut off all communication with her. All you are doing is triggering yourself into ruminating about her. Some people find it helpful to set aside a period of time each day to sit with thoughts and emotions, say up to half and hour. Allow yourself to feel and think during that time and then force yourself to do anything else that will distract you from it all. Clean closets, take care of things you've let slide. You should at least get some satisfaction for having completed those tasks which should also boost your mood. Do nice things for yourself, but new clothes, go out with friends, etc. Make yourself do these things. The next day, sit down again for half an hour and repeat. It will take a little practice, but it should get easier.

This becomes a matter of resolve. Look around you at the things you are neglecting or not doing properly as a result of ruminating and depression. And, think about this, if you had someone who is very close to you and you knew they were doing this kind of thing to themselves, what would you tell them? What would you do for them?