Hope4,
I wouldn't put too much stock in the letter because he is at best in withdrawal, but really just in the fog. However, it is communications and it does suggest what he fears. Interestingly, it seems to me what he fears is your rejection via lack of trust. It also suggests that whatever relationship you had with your Boss hurt him more deeply than you probably understood.
On the whole, if it were me, and I was NOT in the middle of it <img border="0" title="" alt="[Wink]" src="images/icons/wink.gif" /> , I would view it as communications with some clues as to where to go. I believe you did the right thing responding to him and assuring him.
My bet is that if this A is really over once he goes through withdrawal, that you will get a shot at rebuilding this. One never knows about such things, but I do know that you planting seeds NOW may pay off later as he comes out of the fog.
So I would go slowly. By honest with him, work on yourself, and communicate with him. Since I don't know either of you, it is hard to tell what if anything is under the fog talk. But, I suspect there are clues for you in this letter, but they will only mean something to you. The clues will not be about love, but about what hurt him.
You are right this is not a love letter, but in someway right now it might be better. Just depends on the clues to his hurt and feelings about the marriage you can pull out.
I would however, not drive yourself mad with this. Keep the letter, if you constantly hear the same statements or complaints or such, then these are clues.
Hang in there.
God Bless,
JL