Could you tell him that you are just not in a state of mind to talk about what you envision in a separation? If you feel up to it you could offer up listening to what he envisions.
Let him know that you don't agree with his plan of separating, but you know you can't control his choices and you can't stop him. Maybe ask for a given amount of time to get yourself into a state of mind that you feel you can handle those discussions in.
You don't want to look to him like you are pleading with him.
I don't know, just some random thoughts...
Nature Girl M 40 H 40 M 15, T 19 D11 S9 bomb 3/07 (MOW)