Are you the same as you were 10 years ago? 5 years ago? Even 6 months ago?
I would venture to guess, probably not.
We go through change all the time–sometimes it happens to us, and other times we make it happen. We make new connections and we lose some connections. We change jobs, and likely change careers over time.
For some people, their life partner is the constant throughout these reinventions. A study of partnered people examined the domains that determined life satisfaction over different phases of life (quantitatively: young, middle-aged, and old) and found that partnership satisfaction came out on top overall. (While sex satisfaction was correlated with partnership satisfaction, these were independent domains.) Even as other factors became more or less important as the phases of life shifted, partnership satisfaction was strongly associated with life satisfaction.
As for how the pace of change may vary for people and their partners… well, that’s a question for another day.