“I don’t buy the argument that “people change”. I think “I didn’t actually know who my partner was” is a more likely cause. And there’s nothing wrong with this, but it would be a lot easier to just find out beforehand.”
You are not accounting for the people who deliberately hide their true natures from their spouses. I divorced someone who I had practically lived with (3 1/2 years) before marriage. Raised kids together. Built a house together (tell me that’s not stressful). Had one child get seriously ill. I got seriously, deathly ill. We went through many hard times. We got married and stayed married for about four years until I figured out he was a serial cheater. And when I say serial I mean he had a mental illness. He was sleeping with everyone from people he worked with to prostitutes and strangers he picked up in bars. Game over for me and my children. How didn’t I know? Because he had a job that was very often keeping him late. So it wasn’t unusual for him to be an hour late three or four times a week.
Yes, I didn’t know who he was but the way you worded it it was as if it was my fault. My ex did a very good job of hiding his secret life from everyone from his family to our church members & leaders where we were in a leadership position. So not everyone didn’t do their “work”. Sometimes people just get screwed over.
I wish for you that you have a long and happy marriage. I hope hat no one keeps secrets because that is the biggest marriage killer of all.