Another one here agrees. This is not a mental health issue this is a reality check. He's actually processing some of the feelings/impact. Well bully for him having some feelings. Sounds rather similar perhaps to how you may have felt when all this kicked off back in August? Any sympathy from him towards you back then or was he just busy telling you about the love of his life?
Also agree mental health issues would not cause him to react at all in this way. Maybe disappear completely off the planet for two weeks, and be completely uncontactable etc and then to be distraught as the reality of his selfish behaviour, (daily callous behaviour towards you all I believe) become absolutely distraught at the huge cowardly prick he's been. And then be consumed with shame. But, no, this just sounds like something, I'm afraid, everyone here has experience of when dealing with any selfish coward really.
It really is standard behaviour for someone so selfish and who is used to YOU cutting him slack. That's what he's looking for here - YOU to feel responsible in some way. Lot better than him being responsible for it eh? He'll just pretend oh I think I had a nervous breakdown .. well we can fill you in on the script a bit more when it comes. MAIN THING TO REMEMBER IS HE IS RESPONSIBLE.
I know someone who went through all this and even got referred for bipolar in the end. Psychiatrist opinion was stress caused by marital problem/selfishness in wanting cake and eating it disorder!
Very, very predictable I'm afraid. I don't think he should be there when you tell the children. He's useless. Also please don't think this act continues for BB's purpose.
Please cancel Christmas - this man only thinks of himself. He wants the lunch to assuage his own guilt. Don't provide it.
The last family Christmas together you talk so sadly about this Christmas being, well - I'm afraid you really need to sit up and notice that actually happened last year.
You need to react to what has been happening, look at the distress your children are under, look how H is STILL being a prick! YOU have to make a decision for Christmas not based on him. Your children and you is what your decision should be based on not him feeling he's done a super job of turning up for Christmas lunch!
Your poor children still not knowing why their mum and dad don't act fond of one another any more, don't sleep in same bed etc. They do know really don't they? They might not want to admit it but I'm afraid it's got to be obvious to them.
Good luck