Betrayal??? What do you think?

A strange thing happened today. I was on the phone with my mother, someone who has always been there for me, supported me, been someone I can confide in….and her boyfriend was in a bad mood (bi polar). He seemed a little upset with her about something, and all of a sudden says “maybe I should tell her (me) what you say about her every time she calls.” Her response really surprised me as she said “Don’t.” What could she possibly be saying about me when I call? We have always been close. What did I do wrong? I don’t understand. I feel betrayed. I asked her what he meant, and she hasn’t answered me. My own mother.