Parents’ love for their children can make them do peculiar things. Like staying up until 1 a.m. gluing glitter on a second-grade class project. Or driving 40 miles to deliver a single soccer cleat. Or, perhaps, bribing their teenagers’ way into a fancy college. But one of the weirdest things parents do is love their children more than their partners.

Before you call child services, let me be clear: Of course you have to love your kids. Of course you have to put their needs first. But doing so is also a no-brainer. Children, with their urgent and often tricky-to-ascertain needs, easily attract devotion. Spouses don’t need to be fed and dressed or have their tears dried and are nowhere near as cute. Loving your kids is like going to school–you don’t really have a choice. Loving your spouse is like going to college–it’s up to you to show up and participate.

So why do the harder work for the less adorable, more capable being in your life?

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One reason, actually, is for the kids. Research strongly suggests that children whose parents love each other are much happier and more secure than those raised in a loveless environment. They have a model of not just what a relationship looks like but also of how people should treat each other.

Diary studies, in which parents log their day’s activities each evening, have shown that mishandled tensions between a couple tend to spill over into parents’ interactions with their kids, especially for fathers. Children whose parents are often hostile to each other blame themselves for the fighting and do worse at school, other research has found. In fact, a 2014 survey of 40,000 U.K. households revealed that adolescents were happiest overall when their mothers were happy with their relationships with their male partners. And this is for parents who stay together; the outcomes for kids of divorce–even in the days of conscious uncoupling–are, generally, darker. One of the best things you can do for your kids is love the heck out of your spouse.

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If we ever knew this, we have forgotten. When Pew Research asked young people in 2010 whether kids or a good marriage was more important for a happy life, kids won by a margin three times as big as when researchers asked the previous generation in 1997. But betting all your joy on offspring is a treacherously short-term strategy. Cuddly toddlers turn into teenagers, who greet any public display of warmth with revulsion, suspicion or sullenness. Then they leave. Grown children do not want to be the object of all your affection or the main repository for all your dreams, just as you never really wanted to hear their full toddler recaps of PAW Patrol. If you’ve done your job as parents, one day your home is mostly going to hold you, your partner and devices for sending your kids messages that they then ignore.

Parents can get so invested in the enterprise of child rearing, especially in these anxious helicoptery times, that it moves from a task they’re undertaking as a team to the sole point of the team’s existence. Some therapists say this is what’s behind the doubling of the divorce rate among folks over 50 and tripling among those over 65 in the past 25 years: it’s an empty-nest split.

Gerontologist Karl Pillemer of Cornell University, who interviewed 700 couples for his 2015 book 30 Lessons for Loving, says one of his biggest discoveries was how dangerous “the middle-aged blur” of kids and activities and work was to people’s relationships. “It was amazing how few of them could remember a time they had spent alone with their partner–it was what they’d given up,” he told me. “Over and over again people come back to consciousness at 50 or 55 and can’t go to a restaurant and have a conversation.”

The only way to prevent this sad metamorphosis is to remember that the kids are not the reason you got together; they’re a very absorbing project you have undertaken with each other, like a three-dimensional, moving jigsaw puzzle that talks back and leaves its underwear in the bathroom. You don’t want to focus on it so much that you can no longer figure out each other.

This essay is adapted from the forthcoming book Marriageology: The Art and Science of Staying Together.

This appears in the May 20, 2019 issue of TIME.

Contact us at letters@time.com.