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Kristin Cavallari is opening up about the real reason she called off her first wedding to now-husband Jay Cutler.

"I always go after what I want in life, with men or otherwise, and I never settle. If something doesn't feel right, I act on it. It's just who I've always been," she writes in her new book, "Balancing in Heels."

After dating for a year, the couple split up and called off their engagement in July 2011. They even returned all of their wedding gifts.

"At that moment, something wasn't right," Cavallari explains. "A few things needed to change, and I knew the only way Jay would see how serious I was, was if I ended the relationship."

She reveals that she was "dying inside" throughout their entire break, despite looking tough on the outside. But she knew that she had to be true to herself.

"If I stayed at home, I wouldn't be happy and would probably end up resenting Jay for it," she confesses.

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The estranged pair sought help from a couples counselor. "I credit [our therapist] for saving our relationship," the former "Hills" star writes. "She opened up our eyes to the other person's perspective and gave us great tools for communication. . . . We still periodically see her to this day."

Kristin and Jay got back together in January 2012 and eventually tied the knot in 2013, and are now parents to Camden, 3, Jaxon, 22 months, and Saylor, 3 months.

It all works out how it's supposed to, right?!

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Not only does Cavallari talk about her personal life, but she also spills some secrets from her reality show past.

She admits that a lot of the "Laguna Beach" drama was scripted and orchestrated by the show's producers.

"There was certainly a good deal to the show that wasn't 'real,' but as kids we got caught up in it anyway," she writes. "It was easy to go along with made-up keep things interesting, words were dubbed, scenes filmed months apart were shown in the same episode as though they were concurrent, and phone calls were faked (I would literally be on the phone with no one or sometimes with a producer)."

While the plot was manipulated a lot of the time, Kristin's reactions weren't always fake.

"I was only 17! I had some anger stored up from my parents' divorce and my new stepfamilies, which the producers saw," she explains. "They put me in situations where they knew I would react. I was a fighter back then: When I felt threatened, I acted. So when I felt the producers were trying to break up my relationship, I ended up becoming exactly what they wanted from the get-go...When I acted out, they won."

One aspect of her life that was all real was her relationship with ex-boyfriend Stephen Colletti.

"He was my entire world, and we loved hard and fought hard," she reveals, adding that the show got in the way of their relationship. "Surprisingly, the producers had a bigger effect, as they controlled and mapped our lives more than we were aware. One of the most hurtful things they did was pressure Stephen to spend time with another girl from our show, Lauren [Conrad], while he and I were dating."

To read more about all the drama, pick up "Balancing in Heels" when it hits newsstands on March 15.