In Jessica Simpson’s upcoming memoir, “Open Book,” she gets candid about the real reasons her marriage to  “first love,” Nick Lachey, failed.

In her account of their relationship, Simpson, 39, chronicles their encounter, their chemistry and their fairytale wedding.

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“He was my first love,” Jessica told PEOPLE. In the book, she elaborates on what attracted her to the former boy bander, 46. “Nick loved the fact I was so strong in my faith and that I had this wide-eyed innocent approach to life. When he proposed in 2002, I said yes.”

Unfortunately, the former lovers’ taxing work schedules, in addition to their new lives as reality stars on the MTV show Newlyweds, eventually took a toll on their bond.

“We were young and pioneering our way through reality television, always miced and always on,”  Jessica writes. “We worked and we were great at it but when it came time to being alone, we weren’t great at it anymore.”

“We really got crushed by the media and by ourselves,” she continues. “I couldn’t lie to our fans and I couldn’t give somebody hope that we were this perfect golden couple.”

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After just four years of marriage, they pair called it quits, but despite their inability to make things work, Simpson confessed she has a lot of love for her ex-husband.

“I respect Nick very much. I was really young and my success hadn’t really begun,” she confesses. “He knew me as this young innocent 18-year-old that had never been introduced to the world in so many ways. I went straight from my father to him. Nick’s very smart. He was eight years older than me, but he was also young.” 

As readers know, though Jessica is showing much appreciation to Lachey, they weren’t always on good terms.

In 2015, she referred to him as her “biggest money mistake,” causing Nick’s current wife Vanessa Lachey to be “steaming mad.” 

Now, while acknowledging their meaningful past, she tries not to be impolite.

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“We meant a lot to each other and we always will,” she writes. “I want to be very respectful because I married him for a reason and we were together for seven years for a reason. He has a family now and I would never say anything to disrespect that.”

Lachey and his famous wife, 39, are parents to three children: sons Camden John, 7, Phoenix Robert, 3 and daughter Brooklyn Elisabeth, 4. Simpson also has three children with her husband, Eric Johnson: daughter Maxwell, 7, son Ace, 6 and baby Birdie, 10 months.