I got divorced after 20 years of marriage. It was hell (the divorce, not the marriage). I was the one who initiated the split-up. I was 42 at the time. I had been increasingly unhappy in my marriage for at least 7 years. Among the many mistakes I made was keeping that unhappiness to myself thinking it would go away. Nobody knew. Amazingly, even my wife did not know, and when I finally told her, she was devastated. I don't know if I was that good at pretending, or we were just that disconnected. To this day I don't know how I could have been that miserable for that long and have her so unaware of it.
Anyway, we did the counseling, etc. all aimed at trying to find out what was "wrong" with me. Turned out, what was wrong with me was that I was married to a person I did not love enough to be married to. And my "ah Hah!" moment was when I realized that for me, the only reason to be married to a person is because you love them enough to want to be married to them. Not fear of financial consequences, not "for the children", not because you don't want to burden your parents or your friends, etc etc. My ex is a fine person, and that just made it harder. But, 20-some years later I am convinced we are all better for it. Our kids have recovered, have good relationships with both of us, as well as with our subsequent partners, and now that we are "gray", we are all in a better place. And we both had 20-some years to recover from the financial hit we BOTH took to finance our divorce, so we are now both enjoying financially secure retirements.
It was hell to go through, but I'm so glad I didn't live a lie for another 20 years.
One other note, most struggling marriages put on one face for friends and family, and have another reality behind their closed doors, which is why friends and family are often so shocked when it becomes public that they are splitting up.