My mind was my worse enemy-even once reconciliation had taken place. I kept having imaginary conversations......and it was worse when I was doing solitary repetetive things where my mind could wander. I took to doing sudoku; the harder the puzzle the harder I had to concentrate and it took my full concentration. That was the only way I could break the cycle. I would wake up in the middle of the night and do them too.
Re OW, maybe your H is grasping at her as he really knows she is something he should not have. He is obviously NOT comfortable with what he is doing even if he thinks OW is the path he wants. Something inside him is making him uncomfortable.
The wanting to unburden himself at TG to me smacks of 'hair shirt' mentality. Maybe he believes that if he tells everyone about it he will get uproar and somehow he needs the negative feedback. Maybe he thinks it will cleanse him in some way OR it might just help sway his decision making process. Maybe, just maybe, he is wanting the whole family to show him how much they value him and that they don't want him to be involved with OW, and then he has a good excuse to go back and tell her he can't follow through. Whatever his motive, (and I suspect he doesn't even know what it is), it will be a way of him testing the waters with his extended family.
I know you don't want a scene and you want to have as happy a last family gathering as possible, but perhaps you should let him do what he thinks he needs to do. I can only see it as a win situation for you. You are not the one causing this situation and disharmony - he is. He is the one who will suffer from this the most....and then again at Christmas. He wants to be heard it seems. After being silent and hiding things for so long why not let him be heard. Generally it is the making public of an A that kills it.
Saffie me 46 H 46 M in 1986 D20,D18,S16,D13 H's A 01/05 to 07/06 H recommitted to M 07/06 renewed vows 09/06 Going from strength to strength