I admit to being somewhat envious of the letters of appreciation you receive as well. Not because I fault NFP for my marital issues, but because those appreciative couples have a mutual respect and desire for one another, which allows for NFP to enrich their marriage further. I imagine that a big part of their success is that they share in their love for one another by being affectionate and, dare I say, flirtatious even. The effects of which tend toward an appreciation of their partner and a desire to please them for their own sake.

Perhaps you can do a service for your more vulnerable couples by reminding them of the importance of having an affectionate and physical relationship with their spouse. To not have the security of knowing that your love and desire is reciprocated, one becomes hurt, harbors resentment and is assailed by temptation to unchaste thoughts. If someone is indifferent to their spouse emotionally or physically (or both), it destroys the soul of their marriage. Sure, by the grace of God, many of us struggle on, but it is still a horrible and unnecessary cross that we bear. 

I know that my spouse dismisses the importance of affection and physical desire, and she has stated that her disinterest is not an indication of lack of love. However, as the spouse who has his affection and desires rebuffed and as the one who is deprived of that acknowledgement of appreciation or acceptance that accompanies a spouse’s affection or mutual interest in pleasing, I can tell you that it sure feels like unrequited love. The disinterested spouse may be totally oblivious to the damage being done to their marriage, to their spouse and even to their children by their indifference, but I could write volumes on the negative consequences. Without God, my marriage would probably be another divorce statistic by now.