The heated exchange began when Gus recalled the time Nilsa introduced herself to his ex girlfriend Lisa.
"And the first thing [Nilsa] says is, 'You know, me and him used to f---, right?" Gus detailed.
Although Nilsa said those were "not the exact words" she used, Codi appeared to back up Gus' claims, saying Nilsa did mention the pair "hooking up."
"Then we came back into the house in St. Pete, where she started the rumor that me and her slept together while I was dating Lisa, which wasn't true either," added Gus.
Nilsa clapped back, "I didn't start that rumor. You said, 'Hey, I'm hearing that we hooked up.' And I said, 'Well, didn't we like kiss? And you're like, 'No.' And it was squashed. I never said anything else about that again."
Gus argued Nilsa was trying to be "dramatic" and acted like he had cheated. Claiming she didn't treat him like a friend, Gus admitted he held on to "that hate" until their latest season in Montana.
"And when I tried to get that off my chest, everybody got mad at me then too. That's why I was so frustrated. I just felt like it was such a double standard."
At this point, JWoww jumped in and appeared to take issue with the rest of the cast, saying, "I feel like someone should have Gus' back in this."
Check out what would make Jwoww and Snooki "go to war" with their own roommates in the clip above and then catch ALL the drama of the first reunion episode on MTV's "Floribama Shore" Thursday at 8PM ET/PT.