It's good that you felt you could come back for support when you needed it!
It sounds like such a tricky situation to be in. Whilst trying to think of ways you could 'move on' from her, I found this
website that had some sound advice based on attachment.
Have you spoken to your ex about how you are going to manage having so many mutual friends? It would be good if you felt that you could speak to them without 'putting them in the middle', perhaps this is something you need to discuss with your friends.
Could you try to arrange to meet up with a close friend you haven't seen for a while?
I really hope you make it through without relapsing, try to remember all the reasons you stopped and how counter-productive self harm is.