In case anyone is curious, here's what he said when I asked if he could type up the sort of reassurances he shared yesterday, as I apparently wasn't in a place to take them in at the time (I didn't mention his seeming robotic).

"I’m sorry that this has been so difficult for you, [LT]. This change will be a challenge that we can address and get through together. Regarding the fish, I do want you to know that my intention to approach furnishing the office with a clean slate is not in any way personal to you, a reflection on the fish itself, or a rejection/abandonment of you. I value our work together, care about your welfare and wellbeing, and am committed to supporting you, your mental health, and your growth."

It helped to hear him say it would be a challenge we'd get through together. And some of the other stuff. But the figuring it out and working through it together is what I maybe needed to hear. The collaboration part.