I read the message and wondered why his aunt is remembering happy times years ago. Obviously she is trying to hint at his unhappy life now. By simply answering Thank you, he is perpetuating the idea that his life is miserable because of his wife and he, as a good Christian, is staying because it seems the right thing to do even if you are miserable.
A strong man would have taken the opportunity to tell his aunt that he is perfectly happy in the hear and now and wishing her to be happy as well, not living in the past happiness. It was another reminder that a MEM does not change easily, even years of little contact will not help them set boundaries and set anybody in the family straight. They like the idea that they are the victim of a mean wife and receive compassion from the dysfunctional family. He is readily accepted back into the family. He is not the perpetrator, he would never hurt his mem mother, it has to be the wife. It has to be the outsider nobody liked from the beginning. Otherwise their entire narrative they spun around the MEM leaving will fall apart and they would have to face some of the dysfunction. Will never happen, the spouse is and will always be the evil one. Nothing will change that. Cannot change that.