Sir Elton John was "crushed" when he found out his ex was cheating on him and he "fell apart" when the relationship ended.
The 'Rocket Man' star was in a relationship with his former manager John Reid from 1970 until 1975 and the singer has admitted he went into a downward spiral as the romance unravelled.
In new documentary 'Elton John: Never Too Late', the music veteran explained: "I was very naive. I didn’t know that he was having sex outside the relationship. When I found out about it, I was crushed ...
"I had a party at the house, and we had a fight, and he smacked me in the face ... I loved John a lot, but I said: ‘I can’t go through this anymore.’ And when that fell apart, I kind of fell apart ...
"John left an emptiness within me. I thought being alone was a sense of failure. Why isn’t someone with me? I’m not good enough. I chased relationships. I chased love - always looking for love all the time."
Elton - who is now married to filmmaker David Furnish - went on to reveal he poured his pain into his songs after the split. He said: "When I wrote those songs I was miserably unhappy. hat kind of came through in the songwriting.
"It was very very moving to me, and it was very very cathartic."
Despite the split, Reid continued to manage the singer's career up until 1998 when they parted ways professionally.
Elton went on to marry David in 2014 after 21 years as a couple and they are parents to sons Zachary, 13, and Elijah, 11.
The music superstar recently acknowledged that while he has had a "groundbreaking" career in music, it is "more important" to him that he has been good to his husband and his children.
Speaking on 'Good Morning America', he explained: "My music speaks for itself. My legacy is that I was a great husband and an even better father.
"The music, the career is fantastic. It's been mind-blowing, groundbreaking But the most important thing to me in my life is making sure my children are happy, they have a wonderful life and that I was good to them. That's all that counts."
