Enraged and cheated.
What's wrong?
I heard my mother on the phone telling some random "friend" of hers loads of personal secrets about me and my siblings. That and she stank of alcohol, which she said she quit ages ago. She has a history of being a real bitch but I thought that had changed . It'd be alright if it was a friend who was doing this to me, but I'd expect a level of trust and respect from a parent.
I agree with you about how horrible it is to have a parent betraying you in this way, but I think it would also be a bad thing for a friend to do as well.
One time I got really angry with my mother for telling a best friend of hers something I told her in confidence. She was a very good mother otherwise, though. I think the excuse she gave was that she was concerned about what I told her and she needed to talk it over with her friend.
I have no idea what your mother's excuse might be, but she did the wrong thing on at least two different counts.