Alison, repeat after me it will get better.It will get better....
"This will be the 4th Christmas that has been ruined."
Not Christmas yet soooooooooooo don't let it be ruined.
Make it low key, no expectations, have it on Boxing Day,don't have it at all.
Go off and help at a drop in centre, take the kids. Invite some guests for dinner, anyone living alone near you.
Set a place for Abraham at the table.

I know it is so hard to be in what you perceive to be a rock and a hard place. But it won't change until you do-how????
Ah now thats all I got so your homework is......

If all else fails, bacon butties all round and stay in bed clutching a bottle of your favourite.