Jessica Simpson is speaking out about her former relationship with her ex, John Mayer.

In her new memoir, Open Book, the singer and fashion designer is not holding back when it comes to the musician, who she met in 2005. The musical duo first bumped into each other at a pre-Grammys party, and according to Simpson, Mayer then began writing her notes. Following her split with husband Nick Lachey in late 2005, Simpson began to date again. That's when Mayer told the "With You" singer that he "wanted to have all of me or nothing."

"Again and again, he told me he was obsessed with me, sexually and emotionally," Simpson writes in her memoir, via People.

Though they had an intense connection, Simpson admits that she felt insecure about not being "smart enough" for Mayer.

"I constantly worried that I wasn't smart enough for him," Simpson tells readers. "He was so clever and treated conversation like a friendly competition that he had to win."

As Simpson writes in the book, this feeling of insecurity led to drinking.

"My anxiety would spike and I would pour another drink," she shares. "It was the start of me relying on alcohol to mask my nerves."

John Mayer, Jessica Simpson, 2005

L. Cohen/WireImage for J Records

In 2010, years after his relationship with Simpson ended, Mayer made headlines when he called Simpson "sexual napalm."

"Yeah, that girl is like crack cocaine to me. Sexually it was crazy," Mayer told Playboy in an interview at the time. "That's all I'll say. It was like napalm, sexual napalm."

Reflecting on the "shocking" quote, Simpson says, via People, "He thought that was what I wanted to be called. I was floored and embarrassed that my grandmother was actually gonna read that."

Simpson also adds that Mayer's interview made it "easy" for her to walk away from the relationship. After reading his quotes, she erased the "Your Body Is a Wonderland" singer's number.

In her memoir, Simpson, who is now happily married to former football star Eric Johnson, also opens up about her sobriety and recalls the abuse she suffered as a child. You can read more from Simpson's memoir when Open Book is released on Feb. 4.

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