I'm sorry you're going through this! I can relate to a lot of this, as I recently broke up with my T. Different situation, thankfully minus the sudden distance and coldness, but also similar in ways.

From what you write about increasing anxiety going to sessions (and sounds like you never got around discussing this with him?), and the possible diagnosis outside his competence, and how he handled this, I'd say it's objectively better for you to not have this person as your T ... but you probably know that, and it doesn't lessen the pain and confusion.

If you felt something off about him, then something was most likely off. A diagnosis he can't treat is no reason not to give you proper closure - like, at the very least making an effort to reassure you that you're still valued.

Do you think it's worth a try letting him know how this lack of proper closure made you feel and ask for clarification? There's a chance he deluded himself into thinking he was acting in your best interest, and if you let him know that very much wasn't the case, he might be willing to listen.