Working (and living) with someone is hard work though movies and stories rarely reveal this.

Society has mutually agreed that if two people don't want to put in the work, they can split. Society has yet to really get to the next step of "living with kids is hard work, so you can just abandon the kids".

This is not to say that real reasons for divorce don't exist, but there are those who use it as the "easy way out". It's interesting that everyone's ex is the absolute devil, even if they happen to be currently married to someone else's ex.