There are times in life that require new direction to be taken. The reasons can vary, however, I suggest that most will condense to not having fun any more. I have heard it said that laughter is one of the first things couples share. It is also one of the first things to disappear in a failing relationship.
It can happen when one person mentally leaves the relationship for myriad, rational reasons. The challenge in our society, which is based on an aging population, is that mores are changing due to longevity of life. To wed forever makes less sense than it did in the past. Once the offspring are out of the nest, the protective responsibilities are complete.
We become redundant at some point and continue living unfulfilled existence because we can no longer really experience all that life has to offer without sharing it with the same person year after year. I reason that it is better to cut the losses of monotony and spread wings to fly in all new directions.
Today, I was in one of my melancholy moods, thinking about what keeps me hanging around this dimension. It occurred to me that I am still having fun. When the day arrives that I am no longer having fun, then I will make a conscious decision to cut my losses and head into the next existence, willingly, and looking for the WOW factor as is said of Stephen Jobs on his transition bed.