Happiest couple I know was in an arranged marriage by their parents starting at the age of 9.

They grew up together, went to the same schools, shared hobbies, were fully familiar with each other's extended families, and the future-wife ended up going down the aisle slightly pregnant. They've been together for nearly 50 years, have three kids (one of whom was a friend in high school), and are both thoroughly convinced that American romances are dumb, shortsighted, and a big reason for the country's endemic poverty.

Of course, this family is also stupid rich.

The couples that I see fail are consistently either poor to the point that they can't afford a basic standard of living or where one parent is traveling all the time while the other is stuck with perpetual child care. Inevitably one (or both) cheat, or just have a series of meltdowns that end in a break up.

The handful of couples I know where one partner was closeted or just slow to recognize their own queerness seem to be some of the happiest. The relationships tend to be open or poly, to accommodate one or the other. But neither seem to mind. I even know one couple that did get divorced (primarily because the wife was constantly traveling), but you'd never know it given how much time they end up spending together when she's home.

The "I hate my wife" crowd I do know tends to be the ones that are traveling so much they never really see one another except to deal with some financial bullshit, housework, or kids.