Why does partner want trial separation

Is this totally out of the blue Mambypamby or have you been having some problems ?
The lockdowns and C19 situation have been stressing people and this may be part of the problem. I would get a clearer idea of what is happening with him and set some time scales for when you can talk things through. It's not fair to keep you hanging on.
I'm sorry this has happened and hope you can sort things out.

From what you've posted Mambypamby I agree that it doesn't make sense. You say his children are adults so if they want to see their dad, why should the fact they live in the matrimonial home prevent him from seeing them more often?

Perhaps a trial separation may be something that would benefit you both, I say this because you've posted you "want to just call it a day because (you) can't cope with uncertainty". Could your feelings for him not be as deep as you once thought?

Have you told him how his need for a trial separation has made you feel? If not I think he needs to know. I hope things work out for you.

Hello Mamby, I reckon, like a lot of blokes, he's too weak to tell the truth and basically wants out. He's using lockdown as an excuse. Let him go! Make sure that he doesn't yo-yo back & forth and in doing so, uses you. That'll be the hard bit if you still want him in your life, albeit living apart.
Don't waste too much of your life on him. Stay strong and move on.