"Regularly, like, I think that he would have taken the joke in stride, but I think that just like that on top of the fans saying, like, 'Oh, she doesn't really like you' and all the other stuff, I think that it was maybe just like the straw that broke the camel's back," Kat admitted.
Once Nick removed himself from the live session, he and Kat reportedly fired away at each other in the comments section.
"It was just a little -- and I'll say this because we've talked about it since, so he knows -- it was very childish. It was something that shouldn't have happened, especially on such a public outlet," Kat confessed.
Kat said she and Nick had "a really long talk" after their argument and the conversation resulted in them choosing to part ways.
"We both decided that it was best given the current stressors, that it wasn't a good time to really continue our relationship," Kat shared with the magazine.
Now that almost two weeks has passed since their split, Kat insisted she and Nick are "on great terms" and still text, call, and FaceTime each other.
"He's still one of my best friends. We still talk pretty much every day," she insisted.
Kat and Nick's relationship clearly took a dramatic turn this month because Nick just gushed about the blonde beauty March 27 on Instagram.
"I need this coronavirus to be done so I can get my girlfriend back," Nick wrote at the time.
"Miss her so much. Thanks for making my heart beat different when I'm with you."
Big Brother viewers were initially surprised to hear about Kat and Nick's relationship in the jury house because they had sparred while competing for the $500,000 grand prize on the CBS reality series.
But the pair had a lot of chemistry on-camera and were very touchy-feely with one another, so it became pretty obvious romantic feelings were involved.
After Big Brother wrapped its 21st season and Jackson Michie was crowned champion, Kat and Nick reportedly spent time together with their fellow cast members in Las Vegas, NV, in September.
Nick then seemingly confirmed their romance on Instagram in October 2019 when he posted a cozy photo with Kat at the time.
"I love our 'genuine friendship,'" the therapist captioned the picture.
Kat told Us one month later she and Nick then spent a few days together in Los Angeles, CA, before Nick headed back home to New Jersey. They subsequently traveled back and forth to see each other until their eventual breakup.