Dad dropping freshman daughter at college promises to keep it together. He won’t.

Over lunch recently, I asked my 19-year-old daughter if I could write about her starting college in Massachusetts in two weeks after a gap semester.

“Oh, let me see,” she said, putting down her fork and affecting a puffed-up journalist’s air: “‘My daughter’s leaving for school, and now the pain is descending.’”

It’s like she knows me!

Revealed as a man of mush and goo, I’ve nevertheless promised my daughter a good goodbye at her university, tearless and drama-free.

After helping set up her dorm room, I’ll probably drop a dad joke, wait for the eye roll, then entangle her in a brief sort of dude-hug, not so much an embrace as a clumsy hand clasp with a light back slap. Text me some time, I’ll say with a controlled nonchalance.

My daughter is dubious. “I love you, dad,” she tells me. “But when it’s time for you to go, you’ll be a mess.”

I can’t help interpreting my daughter’s enthusiastic eagerness to leave Salem County as a negative referendum on me.

“Not just you,” she tells me, smiling. “New Jersey, too.”

Young people her age are “lions on leashes,” writer Rachel Cusk says, seeking what New Yorker reviewer Anthony Lane calls the “rapturous promise of uprooting.” My daughter’s engines are revving while mine cool down.

This is healthy.

But as the number of her remaining days at home dwindle, I feel compelled to fill the time with conversations of Weighty Consequence instead of simply living the hours, and letting the kid watch Property Brothers.

Also, I’m avoiding listening to music so that no particular song is tattooed onto my brain and becomes the permanent soundtrack of this unsettled hour.

This is not healthy.

Since her announced departure, my daughter’s life has been flashing before my eyes.

It’s 2004, and I’m cleaning my house for two days in anticipation of a visit from an adoption social worker. If I don’t scour the bathtub, I believe, I’ll be childless forever.

My former wife and I are on a plane from Guatemala City to Miami, the first leg of our journey home after adopting a 7-month-old Mayan girl. The second the jet’s tires contact the Florida runway, a State Department guy tells me, our daughter will become a U.S. citizen. I feel giddy as the plane descends, anticipating the bump and bounce. When rubber impacts asphalt, I grin like a fool and channel Tom Petty while serenading the infant: She was an American girl.

After divorce, I’m living with my now 2-year-old in a 50/50 joint-custody arrangement above a music store in a tiny apartment that looks like it was decorated by Dora the Explorer: a pink tent in the kitchen that the little girl fills with M&M’s and Band-Aids, and a giant Mattel S.S. Barbie Party Cruise Ship in the bathtub.

We’re together three or four nights a week, depending on the month. I braid her hair (badly); try to reproduce my mom’s recipes (”Is this what it’s supposed to taste like, dad?”); and obey her repeated commands to sing “Single Ladies (Put a Ring on It)” with accompanying choreo until I’m hoarse and grabbing at my hamstrings.

Then comes: long division; travel soccer; AP pedagogy; a BTS obsession; singing alto in the chorus; a boyfriend. She joins the high school stage crew. During one performance, I glimpse her hand for five seconds as she moves a piece of scenery in the dark, and a charge electrifies me like I’ve seen Springsteen at the Wawa.

As I now assume the cliched pose of Downcast Dad With Matriculating Freshman, I relive the many departures of hers I’ve already endured: no fewer than 884 of them, in fact — roughly the number of times she’s left me to go to her mother, once a week for 17 years.

Her partings are foreseeable agonies penciled into the calendar, routine as recycling day.

But my petulant self-pity is nothing compared to the disorienting stress suffered by a ping-ponging child who’d never signed up for two bedrooms.

“How are you, honey?” a Walmart cashier asks my daughter when she is 5.

“I’m tired of going back and forth from my mom and dad,” she says.

I avert the cashier’s eyes.

At least when the semester starts, my daughter gets to store her Dr. Martens in one closet.

When I told my family in 1980 that I was moving to Ohio to work on a newspaper, my mother ordered me to crouch so she could slap my face.

She had created me, she figured; she got to call the shots.

The hardest thing I’ve ever had to comprehend as a parent is that my daughter’s life isn’t mine to control. Dads and moms must learn their place, then shrink it — and shrink it again — so their kids can grow.

I’ll curb my daddy downer vibe to not wreck this sublime and hard-won moment in my daughter’s life.

At least I’ll try.

But like my kid said: My daughter’s leaving for school, and now the pain is descending.