I'm responding to your question to me on the "Guidelines" thread.
You asked had I read trueheart's letter and if it was a good idea to have your WS read it.
I think I've read trueheart's letter, but if it was recent, I haven't. Please direct me to it regardless.
IMHO, as you referred to in your question, trying to educate a WS in foggy denial is futile. In fact, it may backfire. Early in my WS's affair, I gave her a copy of His Needs/Her Needs and she used it to justify her "new found love" and poo-poo our marriage.
So, unless the letter you are referring to is something totally different, I believe you should not expect your H to get anything from it. You see, he's "different." No matter what trueheart says, it doesn't apply to your H. He's a special situation, get it?
Whether or not it will be a significant love buster cannot be predicted. Maybe yes, maybe no. The safe thing to do is nothing, but I encourage you to seek other opinions. It may be smart to keep a copy handy in the case your H's fog clears momentarily, which usually seems to happen to all of them at least once or twice, and then slip it under his nose. The thought here is that during the momentary clearing the risk of LB'ing may be less and maybe something will click to keep the clearing going.
Now, what I DO recommend you do, if you haven't already done it, is to write your own Plan A letter to your H. This is similar to a Plan B love letter, but without the Plan B punch line - isolating the WS from the BS. Many BSs have done this and it makes a lot of sense, but is not guaranteed to be any less a love buster than any other attempt to educate. It's appeal is the personal, emotional touch.