Marriage/long term coupling is not "natural" but normal in society

With the decline in religious attendance has come a decline in marriage; from 70%+ to 50%ish over the last couple generations

But divorce rate has declined so those that do marry seem to really want it; in the before times though it was how women survived

Coupling fits with biological imperative to have partners but longterm/for life is obviously not necessary since divorce is common too, partners die, etc

That and recent research shows long term married couples are 50% more likely to develop dementia; an imbalance in effort develops where one becomes codependent and forgets how to live and the partner in charge loses grip of themselves and taking care of their partner consumes them.