What I have gathered is that as long as you want to try to save the M (why else would you be here, right), you do not want to do something that makes it easier for them to leave. I do not think you did anything wrong. What you did is not pursuing (although in the future, you should probably have said you were going to keep the car and left it at that - he knows your position re saving the M and trying, no need to repeat that).
The point of not pursuing is that that behavior is not attractive. Your actions and words need to convey that you are calm, confident and are not pushing him in any way. Now, that does not become a doormat. But, what you are trying to communicate to him is that you realize you cannot control him or make him stay. And you cant. The book goes into much more detail on this (Acting "As If"). What you are going to try to do with your actions - not words - is to become a wife that only a fool would leave. In the process you will become a better person.
Keep plowing through the book. Which one are you reading - Divorce Busting or Divorce Remedy? Both are good.
