Now usually, when W brings up leaving/divorce, respond with a constructive positive response like "that will not bring long term happiness" or "I will continue to work on this marriage myself but it would be much easier and faster if we worked together" these constructive snippets came at the suggesting of a DBer who, from what I read, normally suggest the tough approach.
This is where I disagree with Allen, OIN, for whom I have the utmost respect. As pro-marriage as I am, I just think there comes a point where "enough is enough," where the emotional damage by staying outweighs the fight for the marriage. And you get the DOUBLE benefit of that it can be THE most powerful weapon in your arsenal (but one that you CANNOT bluff, you must TRULY be ready to walk).