You did very well. Don't respond to that negative email. He started the problems and now he wants to see you crying over him and begging not to leave you. As you said, he's immature.
If he asks why you didn't respond, tell him you won't reply when there is a no-win answer. Whatever you would say, he would find something wrong with it.
It is steps such as this that might help get him to open his eyes.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
