I wanted to clear up one thing. Going Dark is not a Last Resort Technique. And you can use LRT whether you are separated or not.
The last resort is simply that. We're talking about preventing divorce, and so the last resort is the thing you do, after which you stop fighting the divorce. When I moved out at W's insistence, for a 3-month "trial separation" that was not LRT. At the end of the 3 months, when I asked her if she would go back to MC, she said no. THEN I delivered my LRT. I said, "If you are not willing to work on the marriage, then I think we should start working on the divorce." I said it because I meant it, it was not a trick. Those were the two choices, and I was willing to accept either outcome. That is a Last Resort.
