I followed your first thread, and I am so sad to see this update.
For me, protecting and helping your DSD, who is young, vulnerable and havign a life crisis is the priority.
He needs to understand that.
His daughter, who has lost her mum, and who only has him and you to turn to, has had to turn to you, her not blood relative, because her only blood relative is abandoning her.
I think I would be telling him, that he failure to be a Dad is the most unattractive thing in the world, and you do not want to be around him any more.
He has bailed out on hie responsibility to HIS daughter and left you to pick up the pieces.
For me, if he now came round, complete change of heart, admitted he had been an idiot, apologised and stepped up to the mark to support dd, then yes, I woudl forgive and try again with him.
As the situation stands, for me the marriage is over.