... She says I am putting things into D4's head, telling her I want to move home, and that Mommy is being mean to me. WHAT?!?! I am NOT doing that - in fact, almost every time I take D4 out to play, she tells me out of the blue she wants me to live with them again.
This also seems to be a classic behaviour, of both the cheating spouse, and the MLC spouse. They couldnt possibly blame themselves for the consequences of their own bad choices... so everything becomes their spouse's fault.
There is sometimes a mantra in DB, about admitting faults, and not arguing with your spouse about faults. For most normally balanced people, having your "opponent" accept blame, has a calming influence. Unfortunately, however, when someone is in the state of mind your wife is in.. accepting fault for everthing, makes things WORSE; it perpetuates her unreality bubble of "it's all dave's fault, I'm RIGHT in separating from him".
It's my personal opinion that when dealing with one of these, it is important to NOT do that so much. If something really is your fault, then modestly admit it(without grovelling). However, if something is NOT your fault... or is less than she is making it out to be... I would suggest calmly, gently, but FIRMLY, standing your ground.
News flash: it is not ALL dave's fault. A fair chunk of it, i'm sure but not more than that. My advice is to admit when you are wrong, but stand up for yourself when you are not.
I think your stand on the phone, was great. I think that sadly, your letter was not so great. probably bad timing for it. if she even reads it, which is doubtful.