Robertson, who recently split from her boyfriend whom she met on Tinder, is hooking up with the race-car driver again, Us Weekly reported in its February 22 issue.
"He's a great friend I like to makeout with from time to time," Robertson, 32, told Us.
Ben Flajnik's ex-fiancee began dating Luyendyk, 34, in October 2012, only days after she called off her engagement from Flajnik, who starred on The Bachelor's sixteenth season.
As Robertson revealed in her memoir I Didn't Come Here to Make Friends -- Confessions of a Reality Show VillainCourtney Robertson, she was feeling "devastated, lonely and pretty vulnerable" when Luyendyk reached out to her in the first few days she was single again.
Luyendyk went over her parents' house with wine and admitted she was his "dream babe" and he had "a crush" on her. The couple quickly engaged in a steamy makeout session before taking it into her childhood bedroom where they had the "best sex" of her life.
"When it was over, I gave him a massage and I could tell he was smitten. 'Will you be my girlfriend?' he joked. He told me he was going to cut all ties with the different women he was seeing. 'That's the first lie you've ever told me,' I joked back. After he left, he posted to Twitter, 'Amazing what can happen if you take a chance,'" Robertson wrote in her book.
Unlike Flajnik -- whom Robertson dubbed "so private, cold and unemotional" -- Luyendyk made Robertson feel safe and understood. She said he was attentive and complimentary. However, once their relationship went public, Robertson said the race-car driver's ex-girlfriend and former Bachelorette Emily Maynard "bombarded" his phone with jealous texts.
Robertson, who received some nasty messages from Flajnik, also met Maynard's ex-fiance Jef Holm, who just happened to be Luyendyk's best friend as well. Robertson thought Holm was a shady-womanizing "bastard," and she didn't like him right off the bat.
"I couldn't deal with this love triangle or quadrangle or whatever I was involved in with Arie, Emily, and Jef," she wrote. "I wanted out, no part of this incestuous Bachelor drama."
Robertson ended their fling but quickly came to regret her decision. The following day, when Robertson realized she wanted Luyendyk back, he was already posting pictures of another girl on social media.
"After sleeping on it, I called Arie and told him I'd overreacted and that I'd love to go with him. 'I don't think it's a good idea,' he said. I was surprised and confused, until I checked Instagram later that night. He'd flown in another girl to take to [a] show and because he just couldn't help it Arie posted pictures of them together," the model explained.
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"I clicked on her name and figured out that he was dating this woman, a born-again virgin, the entire time we were together. He'd often seen both of us on the same say. It was all right there on social media, if I'd bothered to check."
It's probably safe to say Robertson and Luyendyk rekindled their flame a couple of weeks back while appearing on back-to-back episodes of Who Wants To Be A Millionaire to raise money for charity.