Madmeg
I initially agreed with all those who said he was like a petulant child, then found myself with some sympathy for him with small children - cos although I looked after my Gkids when small, it didn't come naturally at all. Then I heard those of you who suggested the start of dementia, and wondered about that too. So I have no real advice, cos all are possible.
What more concerned me was that the OP feels depressed and thinking of ending the marriage. That can't just be down to the current (and re) situation but must be more deep-seated and she needs to question herself on why she feels the need for such a drastic step. I've been dithering myself on this issue for some years - and am still dithering.
Finally, I cringe when people give financial advice about separation and divorce. There are no hard and fast rules about the sharing of income and assets. True, 50/50 is a starting point but it seldom works out that way and a fight might be needed to get a fair share. That won't be easy and the uncertainty could add to the depression.
State benefits ARE there but may people fall just foul of the limits to claim and still can't afford to live independently in any degree of comfort.
Hang fire for a year or two would be my advice. Consider what others have said re caring for the kiddies at your DDs home and see if that helps. Maybe time will improve things.
Firstly please don't trundle out the excuse of 'early dimentia' as an excuse for appallingly bad behaviour, it is not the case and certainly not a hard and fast symptom either! Divorce? Don't be daft, why does everyone have to completely overreact to an old tosspot being pathetic by ruining their own life? If he's always like this and one feels enough is enough, kick him out! OR grow a spine and defend your rights to be a great Grandma!