Everyone changes with time.
One thing people often forget to think of is that as one ages, their health also starts to deteriorate. One's health is critical to the way they carry themselves, physically, mentally, and spiritually.
Sometimes, we don't even realize how much our health has changed and how that has affected our behavior towards our loved ones. If our loved ones do not recognize how our behavior has changed, they too suffer. Other times, if our behavior is brought up, we are in disbelief because we always think we know ourselves best. And then, maybe we do know but we're ashamed to admit it because we are afraid of change.
No one truly knows why couples that do not seem to be compatible stay together for as long as they do. There is always more truth than what the eyes can see and what the ears can hear. Many of them may stem from our own values, principles, beliefs/religion, culture, socioeconomic backgrounds, the simplicity of nature and its connection of life itself...etc. Perhaps, it is all through all of that and beyond that we learn to understand one another. We learn to love each other more deeply, become more passionate in our courtship, and more willingly in spirit to fight together until the end.
Who knows...everyo ne walks their own road and they will learn at their own speed and time.
/suchislife...alas...