The "Us" is a fragile, precious, and rare thing. It's no different than a baby, born into the world, with two people to love and care for it.
We make the assumption that because it doesn't really exist - it's not a corporeal being - and because it's really the blend of two adults, that somehow it will fend for itself.
But the truth is that the world seeks to tear it to shreds from the moment it's spawned. The desires and jealousies of others, rumor, finances and stresses of various kinds, time robbed of it by concerns that seem more pressing... "Us" spends its usually short life in soft and hard assaults, and frequently unattended.
A mother famously sports her mama bear claws for her cub when danger arises. She rises on her hind legs and brandishes every vicious promise she can muster to the threat she perceives. Nobody fucks with her family.
Isn't "Us" family? I mean, to be sure, isn't it the very nucleus of the family? Doesn't it deserve protection as much as a newborn or any other member of the family?
Relationships are not about finding someone with whom you can hang out and get along. That carelessness will end in tragedy. Breakups and divorces happen all of the time. 75th anniversaries occur with such rarity that they're almost unheard of. Nobody gets into a relationship with the goal of briefly riding it to a bitter end but rather in hope of loving persistence. "Us" isn't capable of feeding itself or caring for itself - and regrettably "Us" often doesn't receive the passionate attention and care and protection it needs to grow strong and healthy.
We watch our children with a third eye. We're wary of strangers. Overprotective isn't always a bad thing. We admire people who have a superb sense of parental strength and guidance.
We also celebrate those who surpass decades in marital unity. You don't get to those years without a third eye and being wary of the dangers that can threaten "Us."