Andi Dorfman may have gotten engaged at the end of her season as The Bachelorette, but the 29-year-old's relationship with fiancé Josh Murray, 31, turned out to be a disaster.

In her new memoir It's Not Okay (out May 17), the reality star details the duo's demise, including the moment he found out she'd slept with runner-up, Nick Viall, after she initially told him they hadn't.

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"He was devastated, angry and hurt, badly. I apologized profusely for lying," she writes in her book. "That one sexual escapade would become a power play used by my fiancé to justify his mistrust in me. It would be an excuse to call me a whore."

andi dorfman josh murray getty images

Calling their nine-month engagement "the most volatile and f–ked up relationship of my life," Andi remembers a particularly bad fight they had in September 2014 that resulted in her giving back the 3-carat Neil Lane ring he proposed with.

"It wasn’t until [our plane took off] that he leaned into me and whispered in my ear that he was sorry," she says. "I looked at him only to find tears rolling down his face. I had never seen him cry… It had been one of the worst fights we’d ever had, but I wasn’t ready to lose him."

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In a statement to Us Weekly, Josh says of Andi's claims, “It saddens me and is very unfortunate that Andi has chosen to characterize me in such a negative way. I pray she finds peace.”

We can't wait to get our hands on this book!