“Nothing is working. We hate each other, basically.”

So said Nick Jonas in 2013, when the Jonas Brothers — three siblings who became a global pop-rock sensation — abruptly split.

The pop band’s dramatic breakup is laid bare in the new Amazon documentary, “Chasing Happiness” (out June 4) — just ahead of the trio’s brand-new post-reunion album, “Happiness Begins” (out June 7).

The brothers agree that their path to “Happiness” wasn’t an easy one.

“We literally spent a year basically doing therapy, working through some things and figuring out what this chapter would look like,” said Nick on “The Late Late Show with James Corden,” announcing the reunion. (The trio’s “Happiness Begins” tour will include stops at Jones Beach Theater on June 14, Madison Square Garden on Aug. 29 and 30, the Prudential Center in Newark on Nov. 22 and Barclays Center on Nov. 23.)

Jodi Milstein, a West Coast therapist who specializes in families, musicians and bands, thinks the boys were smart to seek a psychological approach to their reconciliation.

“Communication is a big [issue]” for bands like the Jo Bros, the former music exec tells The Post. “These guys start out when they’re these young, invincible 20-something-year-olds or [in their] late teens” — and, given the intense environments they’re in, don’t have much drive to develop strong communication skills or to iron out their issues. As a result, resentments “just fester,” Milstein says.

It’s also common for individual members of the band to start to feel stunted by their group dynamic, says Phil Towle, a performance enhancement coach who’s worked with bands like Rascal Flatts and Metallica.

“[It’s important] to include personal evolution alongside your ambition,” Towle says. And while lots of musicians are “ambitious, and are driven by their art to be successful,” it’s really easy to lose sight of yourself and your goals in a group as massive and celebrated as the Jonas Brothers were.

Both communication issues and diverging personal goals played a role in the band’s split, which Nick initiated. In the doc, his brother and bandmate Joe remembers that Nick held nothing back:

“[Nick said,] ‘The band is over, I want to go do stuff without you guys and I’ve made up my mind,’ ” says Joe, who was shocked and took it hard. “I felt betrayed. I felt lied to. I felt angry — numb.”

The bluntness of the breakup spurred the distance between the brothers in the following years. But after some time apart, they decided to give it another go — which Milstein believes is a sign of maturity.

Often, when bandmates get older, “They start to say, ‘Hey, you know what? Let’s do this on our own terms.’ And they’re able to get back together and bury the hatchet and manage it a little bit differently than they did before,” she says.

To reunite the right way, however, requires major change. “You have to do things differently this time,” says Milstein. “Everyone’s lives are probably significantly different than they were,” and it’s important to recognize that.

Kevin, the oldest of the three brothers, intuited this — and told the brothers that if they wanted to get back together, they would have to work through their issues, including the insane pressures of fame.

“We need to make sure that everyone feels comfortable, and just focus on being brothers,” he says in the doc. “[We have to] probably stop looking at [our dynamic] through rose-colored glasses, too, and actually have an open conversation about it.”

Although the film doesn’t actually show the brothers on a couch with a counselor, it does show their homegrown version of a “therapy session”: a fishbowl filled with questions, a bottle of brown liquor and an outpouring of feelings.

“[My] biggest regret [was doing] Season 2 of ‘Jonas,’ ” Nick says during the boozy group talk. “We shouldn’t have done that. [It] stunted our growth . . . It was not the time and literally we couldn’t evolve because of it.”

Meanwhile, Joe, the middle brother, remembers feeling angry at Kevin for prioritizing his 2009 marriage to Danielle Deleasa over the group. Joe tells Kevin, “We felt like your focus was not in [the band] anymore and it wasn’t a priority for you, and starting a family was.” He remembers feeling personally pushed aside: “All of those years, our first love was music, our first love was the band. And so for me as a teenager . . . to see you prioritize anything but, it was bad.”

It helps that, today, the brothers all have wives and are in similar life stages: Kevin has two daughters, and Nick and Joe both wed within the past year. Joe, who’s married to “Game of Thrones” actress Sophie Turner, says he’s now sympathetic to Kevin’s shifting priorities — even though “it took me a long time to understand,” he says.

The brothers are optimistic about their second act — particularly, they agree, because their motivations feel purer now.

“It wasn’t about the money, it wasn’t about the music, it wasn’t about the fame,” Kevin says of the decision to reunite.

“I want a second chance with them so I can enjoy every moment with my brothers, and I can smile more,” says Nick.

They might just make it: A reunion after a long feud, Milstein says, can lead to “a whole resurgence of creativity.”

But that’s only if the guys are truly ready to put the past behind them.

“[They need to not try] to recapture and re-create where they were before,” she says. “It’s a new chapter.”