In her upcoming memoir, Open Book, the 39-year-old singer recalls her first meeting with Lachey when she was 18 and he was 25. The pair continued dating and eventually got engaged in 2002.
“Nick loved the fact I was so strong in my faith and that I had this wide-eyed innocent approach to life," she writes in excerpts released by People. "When he proposed in 2002, I said yes."
She tells the magazine, “He was my first love."
The couple's fame quickly grew when they starred on Newlyweds: Nick & Jessica, an MTV reality show about their married life, from 2003 to 2005. Everything wasn't picture-perfect, though. "I couldn't lie to our fans and give somebody hope that we were the perfect golden couple," she says.
“We were young and pioneering our way through reality television, always miced and always on,” Simpson explains. “We worked and we were great at it but when it came time to being alone, we weren’t great at it anymore.”
Nearly 15 years after their divorce, Simpson reflects to People, "I respect Nick very much. I was really young and my success hadn’t really begun. 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."
She admits, "I didn't know myself."
Simpson says she is now careful about what she says about Lachey, who is married to Vanessa Minnillo Lachey and they share three children. "We meant a lot to each other and we always will,” she notes. “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."
Following their 2006 divorce, Simpson dated others including John Mayer and Tony Romo, before meeting her now-husband, Eric Johnson, with whom she shares three kids, Maxwell, 7, Ace, 6, and Birdie, 10 months.
Open Book is due out on Feb. 4.