The former "The Hills" regular began dating the Chicago Bears quarterback in late 2010 and they became engaged just months later, in April, 2011.
However, the relationship faltered and Cavallari called off the romance three months later. They subsequently reconciled and wed in 2013, and are now parents to three children.
Cavallari has now opened up about what went wrong the first time around in her new book, "Balancing in Heels: My Journey to Health, Happiness, and Making It All Work", admitting something about their fast-tracked relationship just didn't "feel right", reported Contactmusic.
Describing her mix of emotions at the time of their split, she said, "At that moment, something wasn't right. 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.