The star writes candidly about the musician in her new memoir, "Open Book", revealing she fell hard for the "Your Body Is a Wonderland" hitmaker after they met at a Grammy Awards party in 2005.
"Again and again, he told me he was obsessed with me, sexually and emotionally," she reveals in the book, "(but) I constantly worried that I wasn't smart enough for him. He was so clever and treated conversation like a friendly competition that he had to win."
Simpson also notes her battle with pill and alcohol addiction was heightened during the torrid romance: "My anxiety would spike and I would pour another drink," she explains. "It was the start of me relying on alcohol to mask my nerves."
"He (Mayer) loved me in the way that he could and I loved that love for a very long time. Too long. And I went back and forth with it for a long time. But it did control me."
Simpson finally gave up on Mayer after he famously referred to her as "sexual napalm" in a 2010 Playboy interview.
"He thought that was what I wanted to be called," she shares. "I was floored and embarrassed that my grandmother was actually gonna read that. A woman and how they are in bed is not something that is ever talked about. It was shocking."
She adds, "He was the most loyal person on the planet and when I read that he wasn't, that was it for me. I erased his number. He made it easy for me to walk away."
Mayer later apologised for the remark.
These days the star is happily in love with her second husband, Eric Johnson, the father of her three children.
"I never had that kind of connection before," she tells People of Johnson. "He's a very selfless and loving person."