Hey PacLove - Before really getting into what I should be doing, I had written my wife a couple of letters expressing how I felt, my anger, frustration with the situation, etc.
With my WW, it just made her angry and pushed her further away. She felt it was controlling, and trying to tell her what to do.
That does not mean that you won't have a different experience, I think you just have to try to figure out what is it you wish to accomplish by giving her such a letter and does doing so get you closer to your desired end result.
In my case I think it pushed my WW deeper into the fog, and she is further away from me now than she has been since the BD back in early April.
Just my two cents, I'm sure others out there may have different opinions.
_____________________ Me:44 W:44 Together 22 Married 21 S 19 D 17, 15, 15. 7 EA/PA suspected 3/30/2016 EA/PA confirmed 4/5/2016 ILYBINILWY 4/5/2016 WW asked for Divorce 5/8/2016 (WW has backtracked)