In the second season, which dropped on Netflix on Wednesday, Mattei, 30, and Kaiser, 31, were one of five couples introduced on the show.
The couple has been together, on and off, for four years and Mattei is ready to get married so he issued Kaiser an ultimatum.
While Kaiser makes it clear she loves Mattei, she says there are boxes he doesn't check off for her in terms of his lack of ambition.
Kaiser is also extremely career-focused on her business Pasted Nip and craves a partner who can understand that entrepreneurial drive. So it's no surprise when she connected with fellow contestant Alex Chapman, 32, who has also owned his own business in the past.
During Episode 3 titled "The Choice," the couples sit around a table and explain why they are choosing their new partners. While it's awkward to watch, one can only assume how hard it is to hear your partner hype up another person.
"I choose Alex because I think we're super similar so I think it would be really crazy to live with someone and do a marriage with someone who is identical to me, either it's going to be really bad-ass or it's going to be really terrible," Kaiser said.
She also said Chapman was the "literal perfect person."
Roxanne and Alex with Roxanne's parents in Season 2 of The Ultimatum: Marry or Move On. Courtesy of Netflix.
Although it was painful to hear, Mattei told Narcity Kaiser's decision wasn't a surprise.
"I knew what she was looking for and he was pretty much like the polar opposite of where I was at, at that point in my life, successful business owner, I mean, more than once, he'd already sell sold one of his own businesses, and was doing his own thing again," Mattei said.
"He had this lifetime of experience that she really related with and I was trying to gain that sort of skill set. So I was pretty scared. I was pretty dang scared when I saw that she had chosen officially and then it all became real."
Kaiser, on the other hand, says that part of the show was intense but in the end, she wasn't "too stressed."
"I know that sounds weird. Because I think I was given the ultimatum, I wasn't too stressed about Antonio choosing someone because I think he brought me there to kind of figure out what I wanted and if I wanted him or if I wanted someone else," she told Narcity.
"So in that moment, I think in general it is a pressure cooker moment. I mean, at the end [of] the day even if I didn't feel the crazy intenseness, it is still a weird situation."
While Kaiser and Chapman's trial marriage did start off strong, it didn't end well after Chapman told Mattei he didn't think Kaiser "respected" Mattei.
As for whether Mattei will decide to get down on one knee and what Kaiser will say if he does, those answers will come on Aug. 30 when the finale and the reunion are released on Netflix.
Nick Lachey with the cast of Season 2 of The Ultimatum: Marry or Move On. Courtesy of Netflix.
