I have read your last thread and this one. I see that your H has his point of view and will not consider any other. So there is not much point in arguing the finer points of things. But, Retrouvaille is presented to appeal to a Christian, not Catholic, audience. I think it says on the website that it is Christian-based. I am Jewish, but I got so much out of this program that I don't hesitate to recommend it. I understand, he has his reasons and they can't be changed. I do think that is too bad.
My husband and I were Katrina victims. Three trees fell on our house and smashed huge holes in the roof. We often compare how we felt when our home was destroyed to how we felt when our marriage was terrible. I can tell you that if I were stranded in that house after the storm, and a rescue boat or truck came along with a cross painted on the side, I would not hesitate for a moment to get in and take the help I was offered. I would not say, "no, I have to be rescued by my own group." I think that people who truly want help will take it wherever it comes from. So what that says to me is, he really doesn't want help. He doesn't want to solve this problem.
You cannot do it alone. In your last thread you said you would rather be alone than be subjected to the verbal abuse he gives you. What has changed? Why are you now willing to go to any length to save the marriage?
The one point I made over and over to my husband when we were in the misery, circular argument, venom-spewing stage that you are in now, was that it is a two-way street. Both people have to make an effort. Both people have to change.
I think he did spew a lot of venom in that letter. Maybe that will clear the air for him. However, if he wants to spew more venom at you, I would tell him that you heard him loud and clear, you understand, and you take it to heart. When you are both ready to work on the marriage, then you will do everything you can to make it work. But just one person? He wins; you lose? Only if that is a choice you are willing to live with the rest of your life. It is your decision.