The reality star says on an upcoming episode of Kocktails with Khloé that Harden, whom she broke up with earlier this month, wasn't faithful during their relationship.
"You know, I just don't want to put up with people that, you wanna be monogamous but then you're not monogamous," Kardashian tells guest Lisa Rinna in a sneak peek video.
Kardashian, 31, goes on to explain of the 26-year-old Houston Rockets player, "I've always said – it's long distance, it's this or that – I've always said, 'We don't need to be monogamous. There's a lot of s--- going on in both of our lives, you live in Houston, I live in L.A., we'll see each other, when we'll see each other.' "
She adds, "What girl says that and the guy says, 'Oh,' like, why wouldn't you say, 'Oh, that's great.' "
The reality star, who began dating Harden last summer, says that the athlete insisted he wanted to be "committed."
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"I wanted it but I wanted to be realistic," Kardashian says, noting that she thought asking for a serious relationship was "unfair" considering her busy schedule and estranged husband Lamar Odom's near-fatal October overdose and subsequent hospitalization.
But, she says, Harden "sought me out. He wanted to be committed, then, wasn't committed."
She teased, "and I got the receipts to prove it."
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On this week's episode of the talk show, Kardashian opens up to guests JoJo, Carmen Electra and Ross Mathews about her relationship with Odom, who recently made his first public appearance since his hospitalization alongside the star.
When Mathews asks if Kardashian would ever consider restarting a past relationship, she said, "I hope that first marriage could happen again, but it's really hard to erase everything that happened. Just building a friendship back is what I'm doing now, it has nothing intimately, nothing at all, just pure love and I want someone to learn how to love themselves again."
Find out more about Kardashian and Harden's break up on the March 2 episode of FYI's Kocktails with Khloé at 10 p.m. ET.