If you feel the need to write a letter, do so, but do not give it to him. Burn it after you are finished. Why? Because no matter what you say or do, everything will be your fault. The less you interact with him, the better.

He will play nice as long as he is getting what he wants. He will attempt to engage you, no matter if it is positive or negative, just to be able to say "see, she is still at it". Just leave him alone as much as you can.

Your h is gone, your marriage is dead and you need to mourn the situation. Once you have a better grasp of what is going on, you'll understand more about the "projection" that they use to place blame on us when they are actually doing whatever the deed or statement that has been said.

Again, leave him alone, do not engage unless it is to discuss your family. Do not share your business with him. If you go out, don't tell him where you are going or when you'll be back. The less you say, the better. He needs to hit the brick wall a number of times before he realizes that life exists, bills exist and responsibilities exist and that you are not his mother.

Please, please try to keep the focus on you. I know it is difficult, but you need to live your life to the fullest right now. Trust me, your anxiety level will go down when you start focusing on yourself and what you want to do with your life since he's MIA.