I'm a little late to the party, so I'll not share much of my experience. But I have recently split completely from my T due to her work commitments, and it has been an agonizing rollercoaster of emotion.

Expect to feel every possible feeling, twice. And again. Allow yourself to feel those feelings as often and as deeply as you need to. It's very important.

Find yourself a new T as soon as you can. Not to replace, but to deal with the loss if nothing else. I immediately found a new T to help me, and it was very effective in managing my grief and processing. She was completely on board and not at all bothered by helping me get through losing T1.

I am two and a half months out, and while I still think of her every day, the crushing pain is mostly faded except in rough times. Everybody heals differently, but know this for a fact: you will survive it, the pain will fade, and you'll be okay. Hang on.