I was in a relationship for 4 year that meant the world for me! I would literally die for my partner without even thinking if it's worth it or not, but it ended and not by my choice. My advice to you - if it's over then make a decision to let it go, stop the contact. You won't be good friends now, if you want to try to be friends, try it few years later after no contact but just think if you really need that friendship because it might hurt very very much. The less you know and see and hear, the less pain you feel. I know it is hard and you can't just pretend like this person means nothing to you and he never existed in your life but unfortunately usually it gets to a point when it is so bad that you gotta bring yourself back to life and nobody can help you but you. Even seeing a therapist would be one of the decisions you need to make.
But trust me, everyone who went through this probably will agree that you are better of not talking to her and not seeing her, when it's over then it's over and you need to do everything it takes to survive.
Take care

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