For me, sinking my cock-a-doodle into the same twat for a few years results in total apathy towards fucking that pussy. I cannot even imagine being with the same woman for decades. No wonder men cheat and/or pursue porn with fury.
It sucks because I'd love to not have this derail my desire to maintain a very long-term realtionships, but we are animals, after all.
Humans are not supposed to live NEAR as long as we now do, on average. Natural death by the mid-40s or getting eaten by a tiger before this age is the natural cycle. So what I am saying is, to be "married" to a single female for several decades is totally out of whack. Hell, marriage itself is totally out of whack, for so many reasons.