You can only have your heart broken for the first time once per lifetime. Maybe your first girlfriend breaks up with you, or your favorite band breaks up, or your family pet takes a final trip to the vet.

Or you discover professional sports is as cold a business as any other.

“It’s that time again, isn’t it?” Howie Rose, longtime Mets broadcaster, eternal Mets fan, said the other day. His face told you: Yes. Yes, it is that time again. Forty years ago Thursday, the Mets traded Tom Seaver to the Reds for four prospects who became four undistinguished players. This is the story of how that happened. And how, 40 years later … well, let Howie tell you.

“I still feel it,” he says, tapping his chest. “Right here.”

The first warning shots were fired in spring training, 1976.

Baseball was undergoing a revolution. Free agency was real. Across the sport, players were playing out their options, meaning that after being renewed based on their prior salary, they would be free to play for the highest bidder.

Tom Seaver went a different way. He signed a three-year deal at $225,000 per year. It seemed a splendid deal the moment he signed it. He was wrong. The first free-agent bonanza hammered that home. Wayne Garland — lifetime record: 55-66, 3.89 ERA — received a 10-year, $2.3 million contract. There were other indignities.

Seaver grumbled, but his most pointed arrows were at the fact the Mets’ front office hadn’t made a serious effort to recruit any free agents — notably Gary Matthews, who left the Giants for the Braves. Seaver griped. He was told to pipe down. Indirectly, that message was sent by M. Donald Grant, the chairman of the Mets’ board of directors.

The more pointed barbs were supplied in the pages of the Daily News by its increasingly curmudgeonly sports editor and columnist, Dick Young, who had spent many years ripping Grant, but whose tune changed soon after his son-in-law, Thornton Geary, was hired to work in the team’s front office.

This was as glorious a time as the New York tabloid wars ever have known. On Nov. 20, 1976, The Post had been purchased by Rupert Murdoch, and his impact had already been felt by the time spring rolled around: Page Six, grab-your-shirt-collar headlines, a distinct editorial recalibration.

Baseball is where the warring papers conducted their fiercest skirmishes in that first year. The Yankees had assembled their Bronx Zoo team, and were a few weeks from their own batch of bloody back pages. But first it was the Mets’ turn.

On May 31, Seaver had told Maury Allen, The Post’s Mets beat man: “My relationship with the Chairman of the Board has deteriorated beyond repair.” Seaver already couldn’t stomach even saying Grant’s name. Grant — through Young — had his reply ready, though it waited a day as he first decided to fire manager Joe Frazier.

“Surprise!” Joe Torre, the new skipper, exclaimed as he walked through the old Shea Stadium Diamond Club door before his introductory press conference.

The next day, June 1, under the headline, “Joe Knows the Score, Nobody Wants Seaver,” came the official declaration of war between team and player. Young quoted Grant: “He has destroyed his market.” Grant called him “a headache.” Then Young took a solo turn: “In discussing Tom Seaver and his problems, we must never mix up the two Seavers. As great a talent as is Tom Seaver, he has become an irreparably damaging destructive force on the Mets.”

Seaver beat the Expos that night, 6-4, his first win in a month. To Allen, he said, “I’d love for the Chairman to call me and tell me what moves we might be making to make this team better.”

In its own way, that provided an escalation. Young, who wielded more influence than any sports columnist before or since in his 40 years at the Daily News (and his final six at The Post), saw that comment and realized he had at least one captive reader, a right-handed pitcher living in Greenwich, Conn. And he pounced.

“If I didn’t write a column there are several guys in this town who wouldn’t have anything to write about,” Young sneered on June 4, a day when The Post’s front page screamed: “‘It’s Not Over’ — Son of Sam.”

The Post, not surprisingly, was happy to take Seaver’s side of the debate, the side on which the overwhelming majority of Mets fans lived. By June 7, it was clear a Seaver trade was more than just bluffs and threats, and fans had started to besiege the Shea Stadium switchboard — a few dozen per day at first, then a few hundred. By mid-June it was all but impossible to get an operator on the line.

On June 7, Seaver shut out the two-time defending champion Reds at Shea Stadium 8-0. It was his 42nd shutout as a Met. He struck out 10 — the 60th time he had done that. When he fanned Dan Driessen in the seventh, he passed Sandy Koufax on the all-time strikeout list, and though there were only 16,067 in the house, they gave such a raucous standing ovation, Seaver had to step off the mound.

Torre, even then the diplomat, said afterward, “I think anyone who thinks the reaction of the fans was aimed at anything but Seaver’s pitching takes away from his performance.” But even Seaver acknowledged: “Some of the problems I have still exist. Hopefully they’ll be cleared up.”

Grant actually visited Seaver after that game, and for a few days, some hopeful stories appeared that maybe the two men could reach détente. The Post’s Allen wrote: “Trade him? One does not dispose of a Picasso for a schoolboy drawing in a moment of blister.”

Young had other ideas. “No one has offered a star yet for Tom Terrific, pacifier and all,” he wrote the day after Seaver’s gem. A few days later, he added: “Seaver has found somebody who wants him. Mets fans.”

In an era before 24-hour talk radio, before the internet, before social media, those fans nervously monitored the papers the next few days, in between catching up on the Son of Sam, on James Earl Ray’s escape from Brushy Mountain State Prison, on Farrah Fawcett being fired from “Charlie’s Angels,” on Led Zeppelin scalpers commanding up to $150 for a triumphant gig at the Garden.

Al Geiberger shot a 59, the first touring golf pro ever to do that. The Nets drafted Bernard King. Seattle Slew won the Belmont. The Yankees climbed into first place. Ray was caught in the woods five miles from the prison.

And on Sunday, June 12, Seaver won his 189th career game as a Met in Houston. The final out was a beautiful tracer of Mets history: With two on and two out, Dave Kingman caught a ball with his back to the fence, foiling a walk-off bid from a 30-year-old Astro named Art Howe.

“There is a strong possibility this might be my last game for the Mets,” Seaver said quietly afterward. “I know they are still talking to other clubs about me. The strong possibility still exists that I will be traded.”

He whispered to Allen, his eyes tearing up: “I hear it’s the Reds.”

“A trade of Tom Seaver — for anybody — would be a final blow to the destruction of a once-proud franchise,” Allen wrote.

Yet for all the momentum that was building for a trade, there soon emerged a sliver of hope. When the Mets arrived in Atlanta, Seaver was told the Mets’ owner, Lorinda de Roulet, wanted to talk. They did, for two hours.

Grant — through Young — had been pushing the narrative that Seaver wanted to renegotiate his existing deal. That was a filthy word in 1977. Seaver admitted he was unhappy with what he was being paid. But he also was PR-savvy enough to know he couldn’t ride that horse and remain viable with working-class fans.

And now Seaver had gone over his head. That was the final straw.

Seaver asked the owner, and general manager Joe McDonald, if they could compromise: He would play out his pact through 1978. But would the Mets be willing to discuss a three-year extension after that, with an eye toward a market-value payout (in the neighborhood north of $1 million)? He was told yes.

Seaver went to bed believing he would be a Met for life.

He awoke the morning of June 15, the trade deadline, walked to the pool at the Atlanta Marriott, and was greeted by Dick Schaap, then working for NBC Sports.

“Did you read it?” Schaap asked.

“Did I read what?” Seaver replied.

“Young.”

Seaver stormed into the hotel, called the Mets’ offices, demanded to have the column — clearly planted by Grant — read to him. It started nasty: “In a way, Tom Seaver is like Walter O’Malley. Both are very good at what they do. Both are very deceptive at what they say. Both are very greedy.”

But the money shot was a 33-word passage toward the end.

“Nolan Ryan is getting more now than Seaver,” Young wrote, “and that galls Tom because Nancy Seaver and Ruth Ryan are very friendly and Tom Seaver long has treated Nolan Ryan like a little brother.”

Seaver demanded he be transferred to McDonald’s office. Before the GM could say anything, he screamed: “Forget what we talked about. Get me out of here.”

That night at just before 11 o’clock, a young Post reporter was sitting in the studio at WMCA-AM radio, filling in for the regular host of the evening sports talk show, John Sterling. The kid had been taking calls all night about the Seaver deal, most of them killing the Mets, killing Grant, killing de Roulet. He was handed a bulletin.

“And I knew,” The Post’s Larry Brooks recalled, 40 years later, “it was about to become really interesting.”

The back-page blood flowed freely. Allen was told to write a column “and let him have it,” and Allen knew his bosses didn’t mean Seaver. The headline blared: “DICK YOUNG DROVE SEAVER OUT OF TOWN” and its final paragraph echoed the melancholy that had seized the city: “It is all over now. The only winners are the fans on the banks of the Ohio. Don Grant and Dick Young ran Seaver out of town. Sad. Very sad.”

And it wasn’t just The Post piling on. At Young’s very own newspaper, he was being filleted. Jimmy Breslin knocked on the door of Grant’s apartment at the Mayfair House at 65th and Park and asked Grant what was wrong with someone wanting to get paid what he was worth. Grant said, “You and I have a difference of opinion.”

Breslin wrote, “Grant befits those who use initials instead of first names.”

The next day, Pete Hamill raged: “[Seaver] leaves behind a diminished city. We lose his talent, of course, and his intelligence. In the disgusting campaign against him in those dismal final weeks, we also lost a huge measure of municipal class. For two years Young has been functioning as a hit man for Mets management.”

Seaver told Hamill: “I guess Young has a huge ego. I think he loves to play God.”

George Steinbrenner gleefully told Page Six: “I would never have traded him. He’s a star. New York is a star town.”

Young, for his part, backed out of the firestorm quickly, his last words on the matter being: “Sure, the fans will be angry. But that will pass.”

He may have been right in the short term. Seaver made his debut as a Red on Saturday, June 18, and shut out the Expos — the same day Billy Martin and Reggie Jackson nearly exchanged punches in the Fenway Park dugout. The Mets had been left in the dust.

But five days after that, Seaver made his home debut in front of 51,864 rabid fans and lost a tough 3-2 pitchers’ duel to the Dodgers and Tommy John. Afterward, he and Nancy were waiting for a Riverfront Stadium elevator. Brooks was behind them in line.

“Is it over now?” Nancy asked her husband.

“I think,” Seaver said, “it’s just beginning.”

Forty years later, ask any Mets fan 50 and older and they will agree with that. It’s still not over. It’s that time again.