Breaking up with someone you love is horribly painful and I know all about the thoughts that constantly run through your head, wondering what you could have said or done differently. If your obsessive thoughts continue for more than a few months, and are interfering with your normal life, consider talking to a counsellor to get it all out there.
Your EXBF may or may not recover, but often when an A is really serious about recovery there's no room for relationships. Breaking off with you, painful as it is, may be encouraging for his future.
You will feel better eventually but for now hunker down, be kind to yourself and don't be afraid to talk to friends and family.