I have to agree. Stop the letters. In his condition they may be doing more harm than good. If you need to, keep a journal about your feelings, and maybe one day you can show it to him. Judging by his response to your letter to your ex, he may be too fragile to see right now. I am going to guess that he was already on the verge of a crisis when he saw the letter, so don't feel guilty about the situation. Just give him time and space, and when he is ready, if it's right, he'll be back.