Tiredofpain, I have read through the whole of your first thread before replying. Two sentences really stood out:
"I am/have always been in the role of playing catch-up."
A man must never do this - it automatically weakens him and thus decreases attraction. A man should do for his wife what he truly should or can, without expectation.
"As hen pecked as I sound, I am a pretty strong personality everywhere else in my life, except with her."
That is a paradox to which only you have the answer. I'm going to go out on a limb here, and suggest that deep down inside you do not believe you are strong at all. You are of course wrong, but that belief has allowed your wife to treat you with disdain for year after year after year. Perhaps you should discover your true and strongest self before you even give your wife that letter?
In your first thread both FijiOrBust (second post) and Martelo strongly suggested you do some reading - did you? If so, did it give you any insight into your current situation? If you didn't, now is the time.
Don't get me wrong - a long-term SSM can be emotionally crippling. It can seem endless and grey and bleak and so ... unfair. But attraction (and life as a whole) is ultimately not about fairness, about rewarding the attentive husband or good father or "nice guy" with lots of sex. You can read my second post to Tyguy in order to get my overall take on these issues - his situation was different and so not all of the points will apply to you - but I think some will.
The most critical question for you right now is: Do I have an innate sense of masculinity, of self-worth, of purpose in the world, that is freestanding and totally independent of whether or not I am getting approval or sex from my wife or indeed anyone else? Judging from your letter, the answer is "no". That weakens you at the very core of your being, and makes you inherently unattractive.
That's not a criticism - just an observation. Due to all kinds of reasons, I suspect very many married men in the Western world would also have to answer that question "no". But the question has to be confronted - it is fundamental to every man. If you ask me, you need some time away from this marriage - a one or two week holiday on your own - something absolutely different, and wild, on the edge. Mountain-climbing? Desert trekking? Jungle exploration? Dangerous experiences that will make you have honest conversations with yourself, rather than tiptoeing conversations with your wife. When you can answer that question "yes" and really believe it, you will never look back. You will never act or speak the same way with your wife again. Your letter will also look very different, although I doubt you will actually need to write one.
"A man can be destroyed but not defeated" - from The Old Man and the Sea, by Ernest Hemingway.
Which I take to mean that every man has within him a spirit of relentlessness and optimism. Its already there; he just has to cultivate it.