Why is it important for him to have a say, like you said is it so he feels like he's leaving you in better financial shape if he leaves, or cause if you stay together, he wants more of a commitment from you financially if you stay together? I know you don't want to mind read, and you certainly cant ask him either. He's obviously not thinking straight yet.
Guess the question was more pointed to the vets, on how you could ascertain some info on why, without breaking some of the rules or progress. After thinking about it, I guess it probably doesn't matter, as bad as he pushed the issue, if he doesn't get an answer soon. He'll either forget about it, or shove it right down your throat again.
I don't envy you, its hard to be neutral/detached/PMA'd when its in your face pushing for answers, that are A. unimportant right now B. Might not have anything to do with him C. Takes your own goals out of your life, as if you don't have a say. D. Comes off as a "Do as I say, not as I DO".
Best to back off a for the next few days, and if he pushes it again, try your best to say "I'm thinking about what I need to do for me, my goals, and my happiness" ???