'The relationship was very complex.'
In an interview that will air on Tuesday's Today show, Simpson tells Hoda Kotb that she and Mayer, who met in 2005 and dated on-and-off for years, had a challenging relationship.
"We were great at intimacy. We were great at loving each other. That was easy, but the relationship was very complex," she explains. "And it was always on-again, off-again. On-again, off-again. And I went back close to nine times."
"He loved me in the way that he could and I loved that love for a very long time. Too long," she told the magazine. "And I went back and forth with it for a long time. But it did control me."
"He’d walk into a room and pick up his guitar and you’d swoon," she added. "I didn’t really know the man behind the guitar. And that was my mission."
Their relationship eventually came to an end in 2010, after Mayer referred to her as "sexual napalm" during an interview with Playboy.
"He thought that was what I wanted to be called. I was floored and embarrassed that my grandmother was actually gonna read that," Simpson told the outlet. "A woman and how they are in bed is not something that is ever talked about. It was shocking."
That the comment, she said, "made it easy" for her to "walk away" from the relationship.
"He was the most loyal person on the planet and when I read that he wasn’t, that was it for me," she explained. "I erased his number."
Simpson noted that Mayer has "publicly apologized" for the comments -- he told The New York Times that he was "far out of touch" in a 2017 interview -- and added that she's grown up since then too.
"I know that he’s publicly apologized and I don’t want to take that away from him," she said . "I think he knows a lot of this about me already but he doesn’t know the perspective I have as a woman. That was Jess in her 20s."
Open Book is due out Feb. 4.
Jessica Simpson Says She Erased John Mayer's Number After He Called Her 'Sexual Napalm': 'It Was Shocking'