What day is your final session? It really shouldn't have been dropped on you like this, but at this point, it sounds like it's going to happen - right? There's no chance of you going with your T to his new office?

It might be helpful to think about what you want to get out of your last session. What do you want to tell your T? What do you want to ask? If I were in your position, I'd be thinking of "what do I need for closure?" and "what am I going to have a hard time letting go of, what am I going to keep thinking about, if I don't say it?"

Take the opportunity to make sure you express your feelings to your T. Even if he gets upset or defensive (and if he does, please feel free to call him out on it. I'd say something like, "I'm sorry that this is difficult to hear, but this is my experience - and I need to express it before you leave." or something like that, however feels right for you.)

For example, you put a lot of work in to that letter, but it sounds like your T didn't really respond to it at all, he kind of brushed it off, and that was hurtful and dismissive. That's something you can express in your last session.

The fact that this whole thing was handled so terribly, and that you are feeling lied to and abandoned (that's what it sounds like, apologies if I have it wrong - I don't mean to put words in your mouth) - THAT's worth expressing.

You might not get responses that you like. But, I really hope he's able to hear you and respond in some way that's helpful and not dismissive, and maybe helps you move forward.

Good luck... *hugs*