So very sorry for that poor girl and for you. What happened was not your fault, not even partially. Your friend was lucky to have you to talk to and you even stood up to her ex and tried to help. If your friend did not have you she would have found someone else to confide in and then that person would have been the third wheel. Her ex was seriously disturbed and would have found another friend or other reason to hurt her if you were not in the picture. It would have happened anyway. Try to hold onto the good memory of your friend as that is your tribute to her. Sharing your story, like you did here, may also help other people to get away from a bad relationship sooner. If I were your friend, I would be proud of you and thankful that you were there for me and tried to help. I'm sure your friend is proud of you too from wherever she is now.