I think if you can come up with an answer to his unhelpful question, that will be helpful.
What could he say to help you- would it be to honor your feelings and share your sadness? Would it be to accept that you felt angry and help you process it? Would it be to offer to see you more until he retired? Or would it be something totally different?

I know his question seems like "Jeeze, what more do you want of me" and we read it as if he's thrown his hands up in the air with exasperation, but you know...

Sometimes, when people ask me questions with attitude, and I answer them honestly, in a heartfelt way without attitude, it gets me a long way.