... I'm going by my assumption that KD is suggesting a constructive tone and content.
Crimson wrote one to his w and they are now going to see a mc to "process" it. So it sure didn't hurt his cause.
ding, ding, ding! Yup...
"first day, last day" principle as the context of the letter. Once done, it's done. No take backs, no regrets, only honest and deep, heart felt authenticity. No blame, no shame.
FWIW Snowman, letter writing is not something that is often recommended as it is seen as pursuing. And as I believe you understand, this letter would in no way be to win her back nor to pursue nor persuade her.
And as always, it is a choice...
One thing that I see a lot of here and otherwise is the complete belief that BECAUSE we did something and DID NOT do something else, those things were the reasons for success or failure.
The reality is, when we set on a path from point A to point B, we will never know the experience nor results of any other path we COULD have chosen.
If there are 100 paths, 100 of them could lead to failure or 100 of them could lead to success. Do or don't do. And if you feel you have done EVERYTHING you could have done, or more likely everything that you are prepared to do and you are ready to throw in the towel... that too is a choice and it is up to you whether the result is success or failure... for you...