A few months ago, you posted that you two had agreed to the duality because it benefitted your son. The prospect of her no longer working with your son was your concern at that time. You wanted her to continue working with him and you said you didn't think you could even continue working with her as a therapist if she didn't continue to work with your son, even though she expressed concern about the duality and didn't feel she could do both.

She decided to continue working with your son which is what you wanted for your son, but she also decided the duality was not working and chose to discontinue the therapy relationship in order to continue working with your son which honestly feels like the professional thing to do. One or the other relationship really needed to end.

It was a messy situation all the way around, and it is sad that it ever occurred in the first place, but the only other option she had was to discontinue working with both of you which wouldn't have been any less painful. I hope if you wish to continue working on your own issues in therapy you can find a therapist who can walk you through that process without the relationship conflicts.