Actually, he can not say anything to her unless she brings it up first, which she well might do. And certainly he can not discuss what you and he did (or didn't) discuss during your session. Did she know you were seeing this therapist?

A long time ago a friend started taking her daughter to another T in my T's office. This friend knew I was in therapy but still, running into them in the waiting room was horrid -- I felt exposed and I couldn't settle in. I cried through many sessions over the loss of safety. My T did everything possible to run interference, including meeting me in the hallway when they arrived ahead of me in the waiting room. Fortunately it was a short term thing for them.

It helped to talk about it. I hope you can too. It is hard to imagine giving up three years of hard work on the relationship, although I think I would be equally upset and distraught.

Take care this weekend.