This is a weird line. You cheated on your fiance, but you are begging your friend not to hate you. Why on Earth would SHE hate YOU for something you did that does not affect her in any way, shape or form? I would like to believe that your friend snitched so you would stop drinking and being miserable all the time. But the fact that she gave you an ultimatum, you actually humored her ultimatum and she went through with calling him to tell him is far too much. It just sounds like she already thought you did not deserve the man; either she is into you or she is into him.
An actual friend would have sat next to you while you told him or maybe hounded you until you did. But she would not “hate” you for being imperfect and definitely would never ever call your husband to tell him something that was flat-out not her business. Find new friends while you are in therapy. You were dead wrong for having a one-night stand on your wedding night, and he was absolutely right to divorce you. But you still deserve the opportunity to get your life together and be happy. Your friend Nina? She is going to make life unbearable for you. Cut her loose, too.