Waste of time. You can't teach an adulterer, and it will make him appear weak and defensive. We also don't want him putting things out there IN WRITING right now, when his wife has repeatedly thrown around the "slander" charge. I'm sure his atty would agree with this.
No, he should keep his communications VERBAL at this point, and very general ("I'm sorry you feel that way." ; "Everything I'm doing, I'm doing to try and save my marriage." etc.).
He needs to focus on doing his legal and financial moves right now, and avoid any further drama that letters like this are only going to stir up.
Puppy
Here's some advice that piggy backs on what Puppy said (every bit of which is spot on). First, truth is always a defense to a claim of slander (spoken defamation)/libel (written defamation). Second, absolutely DON'T put anything in writing she might construe as slander. Let your L do that. We are good for that.
