Among the words of counsel he offered for couples working to keep love and tranquility in their relationship was this piece of advice: The most important words in a marriage are "please," "thanks," and "sorry."
As someone who's been married for going on forty-five years, I agree in general with Pope Francis's guidance. But speaking from personal experience, I would offer that the form in which he gave it might be just a weence simplistic and calls for some expanded explanation and clarification.
I agree that prefixing or suffixing any request made to one's partner with "Please" is an excellent practice. It's a common courtesy that polite people use in public. And being at least as polite to one's beloved as one is to everyone else in the world is a good basis for a good marriage or relationship.
"Sorry," though, I think, can be a little trickier. Of course, apologizing to one's partner is important when one has hurt or somehow wronged, imposed upon, or aggrieved their partner, either accidentally or on purpose. Saying “I’m sorry” is absolutely necessary from time to time in a loving - or, for that matter, any kind of - relationship. But there must be more to an apology than just the words that are spoken. The words must be an expression of feeling.
For example, I once knew a priest who taught at my college and, like most priests, was from time to time called upon to give marriage counseling. One time I heard him advising someone that if a person's spouse is angry at them over something they've done all the person has to do is say, "I'm sorry" and that'll be the end of it because once they've apologized their spouse won't be able to say anything else about it. What this priest meant was that "I'm sorry" is a handy tool for shutting up or shutting down someone you've offended. Which is fine, I suppose, if shutting another person up or down is your aim. But this sort of play is toxic to a marriage, or, for that matter, to any kind of interpersonal relationship.
As a healing balm for any offense, from the smallest, most harmless, to the greatest, most hurtful, "I'm sorry" must always come from the heart. Apologize to your beloved as often as necessary. However be likewise careful not to fall into the habit of over-apologizing, as this behavior is not beneficial to a relationship, for not the least reason that it's downright annoying.
Ah, but the same can not be said of the habit of saying "thank you" to each other. Couples can never thank each other too much. They can thank each other all day long without worry of over-doing it. Quite the contrary: couples should thank each other all day long: "Thank you for remembering to fill up the car;" "Thank you for taking out the trash;" "Thank you for chopping the carrots;" "Thank you for making dinner;" "Thank you for washing the dishes;" "Thank you for walking the dog;" "Thank you for tipping the server so generously;" "Thank you for being a good husband/wife/partner/ father/mother ;" "Thank you for marrying/living with/loving me." For two people sharing a household the daily opportunities to thank each other are endless. Couples should thank each other for the big things and the small things, for the everyday, mundane little nothing things without worry that either of them will ever tire of being thanked. Because saying "thank you" is another way of saying "I appreciate you;" "I notice you;" "I love you."
And who ever tires of hearing that?
And so, expanding upon the wisdom of Pope Francis, I'll say to couples, "Abide in 'Please,' 'Thank you,' and 'I'm sorry.' But the greatest of these is...'Thank you.'"
Oh, and "How you doing?" is nice, too.