I'm with Kalamity Jane, I think your father is pissed because your T got mad at him for his behavior toward you or she is trying to get him to behave differently now. I think she told him "about" you but not anything he shouldn't have noticed himself.

I'd go the 14th just curious to find out why she did what she did, the extent of it, etc. and to walk out on them if I didn't like it. How could you not know it was family therapy? Was there a meeting with the three of you?