Firstly I have just been through the exact same thing. I had to take a step back. You need to pr protect yourself and your own well being. I would make a decision to take a step back yourself and not get involved. You may want to protect your friend but at the end of the day she she has her own mind. Divert conversation anand stop making her relationship the focus of attention. I know you care but you need to not be so involved, for your own sanity.