'Vanderpump' Drama: Jax Is the One Who Cheated So Why's He Telling Brittany to 'Shut Up'?

A sneak peek at Monday's new episode shows the reality TV star going off on his girlfriend Brittany Cartwright, after she tries to catch him in a lie about cheating on her.

After Taylor previously admitted to hooking up with former SURver Faith in the show's season premiere, Cartwright is skeptical about whether it was just a one-time thing or full-on fling. To get the truth out of Jax, she calls him on a girls night with Scheana Shay and Stassi Schroeder and pretends Faith told her it was more than once.

"How many times did it happen with Faith?" she asks Jax over the phone. "Tell me the truth, I have proof. She's here."

"Why is she there, why are you setting me up? Why are you doing this?" he exclaims, totally blindsided. "It's only one time!"

Brittany reveals Faith isn't actually there, saying she would have "stabbed her ass" if they were ever in the same room. "All I ask is for the f--king truth!"

"What does it matter if I did it two or three times? What's the difference between one time and ten times? It doesn't make a difference," Jax tells her ... and that's exactly the answer she does not want to hear. "It changes everything, you piece of s--t," she shoots back. "You are f--king done! You're f--king disgusting, I f--king hate you."

Jax's anger really comes out next, as he screams into the phone, "I promise you I didn't do it. Shut up! I said I didn't do it!

Though it's a pretty brutal fight, the two are currently back together.

"It has been a few months, well, seven months since this happened," he revealed on "Watch What Happens Live" this week. "We're working through it. It's a work in progress. I love her very much."

Jax said he's "absolutely" been faithful to Brittany since the incident took place seven months ago and added that their relationship is "stronger now than it's actually ever been."