I do agree with Tailspin.
Something that helped me was our Prime Minister in Australia who spoke about his marriage ending suddenly. He was blindsided like most of us and said:
She certainly had a right to make that decision. I didn't understand it, and I needed to stop trying to understand it, if you like, and accept it,"
I spent a lot of time trying to understand it. But it is entirely impossible to. My wife withdrew, stopped talking and collapsed. In the end, I wasted so much time trying to understand what happened but my life started getting better when I focused on acceptance.
It was not easy. But my energy focused on acceptance achieved something and my energy focused on understanding did not.
I got stuck on why does anyone choose this. But I suspect for them there was no choice.