Carolyn Elizabeth Cost and Patrick James Sheehan posed playfully for a random photo in March 2013 as their paths crossed briefly at Shroom, an annual high school party held at Frick Park in Pittsburgh.

“We were both in lacrosse pinnies,” said Ms. Cost, 26, then a junior at Oakland Catholic High School, a girls private school that has ties to the all-boys Central Catholic School, where Mr. Sheehan, 28, was a senior. (Seniors at his school ran the event, which was attended by about 50 upperclassmen from both schools.)

“Oakland girls went to their football games on Fridays, lacrosse games and their prom,” Ms. Cost said.

Two months after the party, they met again at his senior prom. Each had attended with platonic dates — she with one of his friends, and he with one of hers — and hung out in the same group.

“I definitely thought he was cute, and happy he was talking to me,” said Ms. Cost, when they ended up at the same after-party. The group watched lacrosse highlights in their friend’s basement featuring Mr. Sheehan, an attackman.

After they learned they lived a street apart, he suggested they run errands together sometime, like returning his rented tuxedo. “We never ended up doing that, but got each other’s numbers,” he said.

Hoping to see him again, she then took matters into her own hands and pretended to be at a Pittsburgh Pirates baseball game at PNC Park one afternoon a couple of weeks later.

“Are you at the game?” she texted from home after spotting his Instagram post of a baseball stadium. “I’m here, too.”

Although he was at a Cubs baseball game in Chicago her ruse worked. He suggested they hang out when he got back. (She fessed-up two years later).

A couple of weeks later he picked her up in his hand-me-down 2000 black Jeep Liberty, and offered her his half-eaten gyro when she said she was hungry. She diplomatically declined. They then took a stroll through the cemetery adjoining Frick Park.

That summer they often hung out on her parents’ deck, and the seventh time when they leaned in for their usual goodbye hug, they had their first kiss.

“We went on all kinds of dates, but it wasn’t official,” he said. “I always wanted her to be my girlfriend, but she didn’t want to put a label on anything.”

That fall she visited him with some girlfriends at the University of Dayton, from which he graduated with a degree in criminal justice. She made it clear, though, that they shouldn’t get too serious.

“She didn’t want to do long distance,” said Mr. Sheehan, who took her to a lacrosse team party that weekend.

Still, the two spent the next summer together and continued to casually date. They broke up when she left for school — Marist College in Poughkeepsie, N.Y., from which she graduated cum laude, with a degree in communications.

[Click here to binge read this week’s featured couples.]

In 2017, during Easter break, they ran into each other at the William Penn Tavern in Pittsburgh. They caught up over beers, and quickly learned that neither was dating anyone. After he walked her home, they kissed good night.

“It was great to see you,” she later texted, adding, “I love you,” to which he replied, “I love you, too.”

They texted constantly while at school, and that summer he visited her every weekend while he worked at a construction firm in Pittsburgh and she stayed in Manhasset, N.Y., while interning with a social media fashion influencer in Manhattan.

In July, during one visit, he pulled out a photograph of Ms. Cost when she was younger, which was given to him in high school by her mother. “On the back he wrote, ‘Will you be my girlfriend?’”

This time she replied, “Yes, yes.”

In September 2019, they rented a tiny one-bedroom apartment on Manhattan’s Upper West Side, and as Covid-19 locked things down they got a Bernedoodle named Bus, after Jerome Bettis, the retired Pittsburgh Steelers running back.

“He took up the entire apartment,” she said, with a laugh. (He was supposed to weigh up to 30 pounds, and now weighs 80). In September 2020 they moved into a bigger place with a backyard in Williamsburg, Brooklyn.

They now both work in Manhattan. He as a construction project manager at KCC Design Build, a general contracting and design firm; she as a fashion publicist at Shadow, a marketing agency.

In October 2021, Mr. Sheehan got down on one knee in Domino Park in Brooklyn under the Williamsburg Bridge as a friend visiting from Virginia took their picture.

On Nov. 26, the Rev. Gregory Elder, a Roman Catholic priest, officiated at Sacred Heart Church in Palm Desert, Calif., before 100 guests.

As the couple walked into their reception at Ace Hotel and Swim Club in Palm Springs, the Pittsburgh Steelers theme song “Renegade” boomed out as guests waved their version of the team’s “Terrible Towels.” Gold terry cloth towels with black block letters said: “Sheehan Wedding 11.26.22.”

“It felt like we had just made the game winning play,” said Ms. Cost, who is taking the groom’s name.