Dianne Cox and Michael Cammer don’t particularly like being married, which is not to say they dislike it. Mostly, it doesn’t matter to them.

Dr. Cox, 64, and Mr. Cammer, 56, had been living together nearly 25 years and were raising two college-age daughters when they exchanged vows in April 2017 in their hometown New Rochelle, N.Y. Now they’re empty nesters who feel equally ambivalent about their walk down the aisle in front of 150 guests.

“We’re happy together,” Mr. Cammer said. “We’re in love.” But, as he noted, “the story here is mostly one of status quo. A happy couple gets married and it doesn’t screw up their relationship.” Neither ever bought into the idea that love and marriage were a package deal, or that one should automatically lead to the other. Their romance has neither deepened nor slackened since they married, they said, and their lives have maintained the same steady parallel they established decades ago. This doesn’t mean they wouldn’t tie the knot all over again.

Dr. Cox and Mr. Cammer are scientists, which might explain their ultrarational approach toward their relationship. Dr. Cox is a professor of anatomy and structural biology at Albert Einstein College of Medicine in the Bronx. She met Mr. Cammer, a microscopy specialist at NYU Langone Health, in 1992 when she was a graduate student at Einstein and he was the newly hired training director of microscopy there.

Months after he attended a first potluck dinner for fellow students at her apartment, they were considering moving in together. But before Mr. Cammer could integrate his belongings into her space she issued a proviso. At 34, she didn’t want to wait much longer to have children. If he was game for becoming a father, great. If he was under the impression that the bridge to starting a family should not be crossed without the clanging of wedding bells, he was out of luck. “Fine by me,” he told her. Their older daughter, Rachel Cox Cammer, now 27, was born in 1995. Natasha Cammer, now 25, came two years later.

The principle behind Dr. Cox’s avoidance of marriage, which started incubating when she was a teenager, may be best summed up by Joni Mitchell. Like the pop star in her 1971 hit “My Old Man,” she felt she didn’t need a piece of paper from city hall to keep her tied to Mr. Cammer.

Her parents, who were married more than 50 years before both died, would have preferred that she marry before having children. Her father worried that Mr. Cammer, whose father was a former litigator who understood family law, would have a custody advantage if the couple split.

But by 2009, when she wrote a New York Post article about why not being a wife was important to her, she had become a flag-waving proponent of cohabitation minus the legal strings. And she was winning admirers among her students at Albert Einstein, especially her female students, for her ideals. “I was the poster child for, you don’t have to get married,” she said.

The poster began to fade on a trip the couple took to Cyprus in June 2016 for a student’s wedding. Mr. Cammer, who had contracted a mysterious infection, was hospitalized their first night there with a potentially deadly case of septic shock. To avoid complications about whether she was legally allowed to sit at his bedside, she told a nurse she was his wife.

Adopting that title for real — she proposed in their New Rochelle bedroom weeks after his recovery from the infection, he thought about it a few days, then agreed — was a way to guard against future catastrophes that might separate them because of murky rules around nonlegal partnerships.

The decision still zaps her twinges of regret. “It did bother me,” she said. “I felt I was kind of betraying this moral stance I had for years about the government being involved in my personal life.” Students who had found inspiration in her choice to commit without the paperwork, she said, were disillusioned. “But I guess I feel that, after 25 years, I had made my stand.”

Six years later, marriage amounts to “an extension of who we were,” Dr. Cox said. Mr. Cammer added, “We rely on each other and expect the security of having each other.” Married or not, they like each other’s company.

Twice a week, despite heavy work schedules, they make time for dinner together. Dates are infrequent but meaningful. Last year, for instance, they saw the revival of the Stephen Sondheim musical “Company” on Broadway. This helped crystallize Mr. Cammer’s feelings about the relationship. “We don’t have the ironic ambivalence and obsessive second-guessing of Sondheim’s characters,” he said. “We’re happy together without ifs, ands or buts.”

“I still find it odd saying ‘my wife,’” Mr. Cammer said. “After 25 years of always trying to figure out what’s the right thing to say — Partner? Paramour? Spouse equivalent? — ‘wife’ should be simple. But my brain stops. I find it weird.” Though they now introduce each other as husband or wife, Dr. Cox also struggles with the title. “It’s a little weird saying he’s my husband after so many years of not doing that,” she said.

Their eldest daughter, Rachel Cox Cammer, now a graduate student in mind body medicine at Saybrook University, never cared what her parents called each other. But she and her sister, bridesmaids at the 2017 wedding, both were thrilled when their parents finally married. Not because they had always wanted their mother to be a “Mrs.” like their friends’ mothers, or for their father to be introduced as her husband. For them, it was more about the occasion.

“My mom and I used to watch a lot of rom-coms, and they have a lot of wedding scenes,” said Ms. Cox Cammer of Peekskill, N.Y. “As a kid I always used to be like, ‘Are you sure you don’t want to get married? It would be so much fun dress shopping.’” She and Natasha, now in medical school at the University of Miami, never doubted their parents’ devotion to each other. “We always respected their decision not to marry. You could always see their love for each other.”

Even so, Rachel won’t follow her parent’s lead. “I knew I wanted to get married at a young age,” she said. On Oct. 13, she and her partner will marry at Candlewood Lake in Brookfield, Conn. The couple met four years ago; they’ve been planning their wedding since August 2021. “We wanted a semi-long engagement so we could refine all the details.”

Mr. Cammer rolled his eyes at news of the engagement, he said. Dr. Cox is happy for Rachel. But “she’s even changing her name, which I was a little surprised at,” she said. Still, they will be there to celebrate, and maybe even to wipe a few happy tears when the couple is pronounced married.

“She’ll have the whole nine yards, all the bells and whistles, including a big reveal about the dress, and I guess she’s dreamed about that a long time,” Dr. Cox said. That’s OK with her parents. “It’ll be a wonderful party,” Dr. Cox said.