The only way i can think about it and not get angry is to accept the view that says they must be SO broken to get to the point where the pain of leaving their kids is less than the pain involved in staying.
After he left, my H used to come around regularly and we would eat together, watch movies and go out with the kids. But eventually, he stopped.
He told me that he got to the point where it was just to painful to continue doing things as a family; too painful to come back into our house. He said he had to focus on surviving and the only way to do that was to stop seeing us.
But it's so hard, especially when there is an OP involved (and how convenient that there almost always is). But again, this seems part of the script of the turmoil/sickness.
I feel for you, I really do.
I cling on to the hope that things will get better with time. That's what keeps me going.