Billy Joel fell in love with the wife of his best friend and bandmate when he was just starting his career.In a new documentary, "Billy Joel: And So It Goes," the Piano Man revealed the anguish he went through when he told his friend he was in love with his wife.Joel had been living with bandmate Jon Small; Small's wife, Elizabeth Weber; and their son, while Joel and Small were in a duo called Attila in their early 20s."I was just in love with a woman, and I got punched in the nose, which I deserved," Joel said in the documentary. "I felt very, very guilty about it. They had a child, you know? I felt like a homewrecker."BILLY JOEL'S FIRST WIFE WALKED OUT ON HIM IN HOSPITAL BED AFTER MOTORCYCLE CRASH THAT NEARLY KILLED HIMEarlier this year, Joel was diagnosed with a brain condition that forced him to cancel all of his scheduled concerts.Longtime collaborator and the executive producer of the documentary, Steve Cohen, told Fox News Digital his fingers are crossed Joel will perform again."I always look at it as a gift when he walks on stage," Cohen said. "I can't predict. I do know that the Billy Joel that I had dinner with last night, that's the Billy Joe that I know. So, look, it's up to him. If he feels like he wants to, you know, play Billy Joel on stage again, we're all gonna be there for him."BILLY JOEL'S WIFE SAYS SINGER'S HEALTH HAS TO TAKE PRIORITY AFTER HE POSTPONED TOUR DUE TO MEDICAL CONDITIONThe five-time Grammy winner, 76, was diagnosed with normal pressure hydrocephalus (NPH), which occurs when cerebrospinal fluid (CSF) builds up inside or around the brain and has led to problems with hearing, vision and balance for the musician."I can't predict whether he's gonna wanna do it. Look, he's got two beautiful kids. His daughter's now turning 10. He's got a great wife. He's got a great life. Like, he's 76. He doesn't have to do s---. And he's giving the fans something in this documentary that they can enjoy more of. So, I don't know, fingers crossed."WATCH: BILLY JOEL'S FRIEND AND COLLABORATOR HOPES TO SEE HIM PERFORM AGAIN AFTER BRAIN DIAGNOSISJoel fell in love with his first wife, Weber, because she wasn't happy with her husband Small.Weber admitted in the documentary she and Small "were not a good fit. We were very young, and we didnt really know much of anything. And I got more and more dissatisfied with the life I was living, and then things got complicated."She and Joel began spending more and more time together."When you just find someone youre comfortable with and can finish your sentences and know what youre thinking without saying anything, sometimes its a low build," she said.Small said Weber was important to him, "but I think I was not the guy she hoped I would be.""I kept seeing that Billy was not the same guy. Something was the matter, and Billy one day came up to me, became a little honest and said to me, Im in love with your wife. So, it was a very devastating thing for me because these were basically my two best friends."Hes crying, and hes telling me he feels so bad, and he didnt know what to do about it. How does he break his best friends heart? But he said she was so powerful to him that it was worth it to him to lose our friendship for it."CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTERJoel said that was the end of Attila, and "that was the end of my relationship with Jon for a while."He said Weber left as well, and he began drinking a lot and attempted suicide twice."I figured thats it. I dont want to live anymore," Joel said. "I was just in a lot of pain. It was like why hang out? Tomorrows going to be just like today, and today sucks. So, I just thought Id end it all."After his second attempt at suicide, Small was the one who took Joel to the hospital."Even though our friendship had blown up, Jon saved my life," Joel said.Small said even though Joel never said anything to him about it, "The practical answer I could give why Billy took it so hard was because he loved me that much and that it killed him to hurt me that much."LIKE WHAT YOURE READING? CLICK HERE FOR MORE ENTERTAINMENT NEWSHe said he eventually forgave Joel."I finally got over it where it was like, OK. He thought it was over for him, but, to me, he didnt even start living yet."Joel and Weber ended up getting together about a year later after shed heard songs hed written about her, when Joel gave her sister a cassette tape of his music."It was all from Elizabeth leaving him, and he was so sad. And he put it into music," his sister, Judy Molinari, said in the documentary."Hearing those songs was overwhelming," Weber admitted. "It was stunning that he could accomplish something like that."Joel and Weber eventually got married in 1973 before divorcing in 1982. He is now married to his fourth wife, Alexis Roderick, after his marriages to Christie Brinkley and Katie Lee.CLICK HERE TO GET THE FOX NEWS APPPart one of "Billy Joel: And So it Goes" premieres Friday, July 18, on HBO and will be available to stream on HBO Max. Part two of the documentary will be released Friday, July 25.