I've name changed on purpose because my DF knows usual username.
My DF is struggling very bad with depression and anxiety and has only recently opened up to very few people recently on the advice of her GP. She has been very honest about the extent to me but less so to another friend and only sharing what she felt comfortable with.
My DF is quite isolated and doesn't have a lot of people in her life which is partly due to her depression and pushing people away. I have found out that her other friend has been telling DF sister who she is no contact with for very good reason, all about her issues and whatever has been confided in her she has relayed. She doesn't see the harm as she says her sister is heartbroken and should know but if my DF found out she would be devastated, embarrassed and would cut Friend off without hesitation because trust is extremely important to her.
I don't know why I should do now. Friend won't stop sharing and even if I tel her to she won't but just won't tell me and then I know my DF confidence is being betrayed but if I tell her she will be hurt and cut this person off and becoming more isolated.