About two months ago, after another stale Saturday night of binge-watching television at their Brooklyn home, Bill de Blasio and Chirlane McCray surprised themselves.

It began with an offhand remark: “Why aren’t you lovey-dovey anymore?” Mr. de Blasio, the former New York City mayor, asked, according to Ms. McCray, his wife.

It moved quickly, both said, into the sort of urgently searching dialogue that had been necessary for years but avoided until that moment: a full accounting of their relationship, what they wanted, what they were not getting.

“You can’t fake it,” Ms. McCray said Tuesday from their kitchen table.

“You can feel when things are off,” Mr. de Blasio said, “and you don’t want to live that way.”

They made their decision that night.

Mr. de Blasio and Ms. McCray are separating.

They are not planning to divorce, they said, but will date other people. They will continue to share the Park Slope townhouse where they raised their two children, now in their 20s — the vinyl-sided hub of a thoroughly modern political family whose mixed-race symbolism helped send a spindly progressive long shot to City Hall.

As with much about their marriage, its strain is imbued with civic resonance, a decade after the pair became what was then the most significant and dissected biracial couple in American politics.

And as with much about their marriage, they see lessons for others even in its tumult, both for workaday couples negotiating the challenges of growing old together and for the small subset who expose themselves to the uncommon glare of public scrutiny.

“I can look back now and say, ‘Here were these inflection points where we should have been saying something to each other,’” Mr. de Blasio said. “And I think one of the things I should have said more is: ‘Are you happy? What will make you happy? What’s missing in your life?’”

It is easy to forget now — after two uneven terms, a calamitous 2020 presidential bid and a decade of slashing tabloid headlines by turns earned and gratuitous — precisely what it felt like to see Mr. de Blasio and Ms. McCray step into power.

They were visually, viscerally distinctive, particularly after 12 years of Michael R. Bloomberg — a living testament, supporters said, to the breadth and promise of New York: Black and white, short and tall, inclined to dance in public. They were so affectionate at news conferences that aides sometimes winced.

Over a nearly three-hour interview, during which they cupped hands sporadically and once high-fived in agreement, Mr. de Blasio, 62, and Ms. McCray, 68, were alternately wistful and upbeat, self-critical and defiant.

Rather than issue a terse joint statement to announce what they called a trial separation — the carefully worded fate of so many political marriages before theirs — the two suggested they wanted to get considerably more off their chests.

They concluded — Mr. de Blasio more forcefully than Ms. McCray — that their marriage would not have reached this place if he had never been mayor, as grateful as they said they were for the experience and as proud as they remain of much of their work. (“Everything was this overwhelming schedule, this sort of series of tasks,” Mr. de Blasio said. “And that kind of took away a little bit of our soul.”)

They cited the Covid crisis — which arrived just as Mr. de Blasio said he had begun seeing a therapist for whom he quickly had little time — as an all-consuming external shock that suppressed more probing discussions of what their post-City Hall lives might look like. (“It made me emotionally very needy,” he said, “and we were not as connected.”)

Yet they also clocked a shift in their relationship a year earlier, they said, coinciding roughly with a presidential run that Ms. McCray viewed with deep skepticism.

“I thought it was a distraction,” she said, publicly echoing a prevalent complaint from Mr. de Blasio’s constituents.

“Kind of true,” he said, laughing. “Point for Chirlane.”

Asked how it felt when Mr. de Blasio proceeded anyway, she allowed that she had to be supportive.

“This is not the kind of thing where you can break ranks,” she said. “That’s part of the difficulty of being part of a package.”

Asked what she was seeking from this new formulation, she suggested that she might enjoy the non-glow of being with a non-public figure.

“I just want to have fun,” she said, adding, as Mr. de Blasio turned to her, “It’s not that we haven’t had fun.”

“Thank you, honey,” he said.

“There’s a certain weight,” she said, “that goes with being with Mr. Mayor.”

It is a perch she came to know well.

Positioning himself in 2013 as a sharp break from Mr. Bloomberg’s gilded bearing, Mr. de Blasio placed Ms. McCray and their family at the center of the race. Their older child assured supporters that Mr. de Blasio was not “some boring white guy.” Their younger one (and his abundant teenage Afro) starred in the campaign’s viral ad.

Tales of the candidate’s courtship of Ms. McCray — when both worked for David N. Dinkins, the city’s first Black mayor — only accentuated Mr. de Blasio’s persistence: Ms. McCray, who had identified as a lesbian and seemed cool to his overtures, relented eventually.

They married in 1994, under a tree in Prospect Park, with two gay men officiating, before a reception with a “Super Freak” dance break and a heap of cannoli.

“He was very easy to fall in love with,” Ms. McCray said.

After Mr. de Blasio’s victory, he was consistently criticized for elevating Ms. McCray to positions of high influence, particularly when a mental health initiative she helped lead was questioned over its spending and performance. He also ruminated openly about her political future, privately boosting Ms. McCray for a potential campaign for Brooklyn borough president. She ruled out a run in 2020.

In the interview, both maintained that the nature of their municipal partnership was obvious from the start. But Ms. McCray acknowledged that there was “no infrastructure” for a first lady seeking a different kind of portfolio, nodding at the burdens each felt in roles for which they could not possibly prepare themselves.

“How can you be a couple in the fullness of what you tend to think,” she said, “when you’ve got this responsibility on your shoulders and you don’t want to add to that?”

While Mr. de Blasio said they had become so secure in their marriage that he had little reason to doubt its strength, unwelcome thoughts could creep in.

One of them, both said, involved their own parents’ difficult marriages. Another was about Ms. McCray.

“For the guy who took the chance on a woman who was an out lesbian and wrote an article called ‘I Am a Lesbian,’” Mr. de Blasio said, “there was a part of me that would at times say, ‘Hmmm, is this like a time bomb ticking? Is this something that you’re going to regret later on?’ So I always lived with that stuff.”

In the 18 months since he left office, Mr. de Blasio has seemed at times to be casting about, personally and professionally.

Last year, he looked in the mirror and did not feel like himself.

“I never anticipated ever doing anything with hair color,” he said of his now strikingly dark close-crop, adding that the current shading is a bit more pronounced than he intended. “But I like feeling what I feel.”

More public was a short-lived congressional run that persuaded Mr. de Blasio that it was “time for me to leave electoral politics.” (More recently, the city’s Conflicts of Interest Board ordered him to pay nearly $500,000 in reimbursements and fines for using his security detail on presidential campaign trips.)

His current endeavors include teaching at New York University and delivering paid speeches in Italy, he said. Ms. McCray has continued to work on mental health policy.

They are both happier now than they have been in some time, they said, taking care to project a practiced warmth inside their kitchen, where Mr. de Blasio at one point wiped something from her face.

A few weeks after their impromptu session amid that Saturday night of television, they exchanged written messages outlining “what we felt about the moment,” Mr. de Blasio said. After that, he said, ground rules were established: “what’s cool, and what’s not cool, and whatever else.”

“One of the things we’re saying to the world is we don’t need to possess each other,” he added.

He quoted two favored phrases of Ms. McCray’s — “Labels put people in boxes, and those boxes are shaped like coffins” and “I never want to be stuck” — and one prized by his brother, a Tibetan Buddhist: “Avoid attachments.”

They will continue to share the home “for the time being,” Ms. McCray said. For now, a photo of the couple in Times Square on New Year’s Eve still greets visitors, which may come to include suitors.

Ms. McCray asked dryly if their phone numbers could be included in the newspaper.

“Can I put a picture from the gym in there?” Mr. de Blasio asked. (He added that he was “not a believer” in online dating.)

As the conversation neared its end, the former mayor pulled out his phone to play a song called “Mango,” saying it might best explain their feelings now.

“I don’t want nothing but you,” it went. “Getting what you need / Even if it ain’t from me.”

Mr. de Blasio hummed a bit from his chair. Ms. McCray danced behind him, gazing ahead.

“Isn’t that beautiful?” he said.