As they say in Elton John’s heyday, 1973 was the best year. He was in the middle of a huge success streak and released his most successful album: Goodbye, yellow brick roadwhich introduced the world to the title song and future classic “Candle in the Wind.”

But the haunting melodies of John’s biggest hits from this period, like this ode to Marilyn Monroe – which John and his songwriting partner, lyricist Bernie Taupin, turned into an ode to Princess Diana after her death in 1997 – reflected John’s inner turmoil reflected at this time. He was in a turbulent relationship with his manager John Reid for five years.

“It was the same time that John Reid broke my heart. “My relationship with him wasn’t what it should be,” explains 77-year-old John in his new documentary Elton John: Never too latewhich premiered on Disney+ on December 13th.

The relationship, which lasted from 1970 to 1975, had a profound impact on John’s songwriting at the time (he wrote the music for most of the songs he released during this period, while Taupin wrote the lyrics) – and also on his psyche.

“When I wrote these songs I was terribly unhappy,” he says in the documentary. “That came through in the songwriting. It was very, very moving for me and it was very, very liberating.”

Reid, 75, was something of a VIP in the ’70s classic rock scene, having also managed Queen in the late ’70s. He is notable for having been featured in both 2018 Queen biographies Bohemian Rhapsody (by Aiden Gillen) and in the 2019 John biopic Rocket Man (by Richard Madden). In the documentary, John describes Reid as unfaithful and “very rough” during their relationship.

“I was very naive,” he says. “I didn’t know he was having sex outside of the relationship. When I found out about it, I was devastated.”

“I was having a party at my house and we had an argument and he punched me in the face,” John continues. “He made my nose bleed and cut my face. I loved John very much, but I said, ‘I can’t take this anymore.’ And when that fell apart, I kind of fell apart.

The relationship took its toll on the superstar, especially after it was over. “John left a void in me,” he says. “I thought being alone was a feeling of failure. Why is no one with me? I’m not good enough. I was looking for relationships. I was looking for love – always looking for love.”

While recording his 1974 album caribouthe sequel to Goodbye, yellow brick roadJohn was introduced to cocaine, which led to a years-long descent into addiction. “I really wanted to be happy and I took the wrong path,” he says, comparing himself to doomed legends Elvis Presley and Marilyn Monroe during this time.

After their romantic breakup, Reid continued as John’s manager until they parted professionally in 1998 after 28 years. In 2014, after 21 years together, John married filmmaker David Furnish, 62. They share sons Zachary, who turns 15 on Christmas Day, and Elijah, 11.

Furnish co-directed the new documentary with RJ Cutler. “He’s really so happy,” Furnish told PEOPLE at the Toronto International Film Festival premiere Elton John: Never too late in September. “When we find ourselves in this moment now, after so much hard work and so much anticipation, emotions are running very high.”

Elton John: Never too late is now streaming on Disney+.