^^
It's not uncommon for couples to separate/divorce after the kids are out of the house, often because they've grown apart. Growing up, several of my friends' parents did this when my friends went away to college.

The couples I know that don't have children and are content are those where both partners have that have given the topic of whether to have children a great deal of thought and have come to the same decision not to.

It's very true, that when a couple is not on the same page, it's a huge issue. You can only ignore the elephant in the room for so long before resentments are likely to build. That is why I split up with my ex and a decade later I look back with no regrets as far as that decision.