It was presumptuous that he "penciled" you in for the DBT group. Very much so, especially since this was only your second in-person session with him and he only mentioned it in passing and you politely said that you might be interested. Hate when Ts do that!

Getting used to a new T is the pits, even after a lousy experience with a T a person has decided to leave! You had two Ts you liked and enjoyed working with. I'm glad you told him you were angry and annoyed. He needs to learn that you know the ropes and you'll express yourself when he steps out of line.

I'd suggest giving him a few more sessions. He might work things through. A really good sign will be him announcing at the next session that he'd actually made the call to your former T. Sure hope he does that!

He might have an autoimmune disease like Rheumatoid Arthritis/Psoriatic Arthritis or possibly MS. With any of those a person can have on again, off again pain or discomfort with movement. He'll be fine if he's up and around and doing his job. Relax, he can handle it! You don't sound too impatient or aggressive, just anxious about wanting to find a good T to work with. Sounds pretty normal to me.