You have been around long enough to know that it is one of the common scripts that they tell themselves (that things will be better in the relationship after the divorce).
This is her divorce. She started it. She is dishonoring you, the kids, herself, the marriage, etc. I hope that she does sign the papers and live through these fantasies quickly so that you can make an informed decision on where you and the kids go from here.
You are just seeing a sick and sad woman who sees her cake coming to an end. If she really felt any more than that, she knows how to stop the madness.
Hoping you find a light in your life each day to survive this.
