Okay, you need to be VERY VERY careful. This COULD involve criminal charges, and you MAY be being set up. You need to contact the THERAPIST. Make an appointment, and SPEAK to the therapist.
First, explain that you COMPLETELY understand doctor/patient, and do NOT want to talk about your son. You simply want to make the therapist aware that you ARE concerned, that you WERE NOT informed this was happening, and IF your son would like, you would be more than willing to meet in a JOINT session, with him, and you and your ex wife.
Why give a "senior" discount, they have had plenty of time to raise the money...