The drama increases during "Teen Mom 2" Season 6 "Special Reunion Part 2," which airs Wednesday, when Leah Messer and Corey Simms argue about their former relationship and his current wife, Miranda Simms.

Messer, who recently completed treatment at rehab, appears surprisingly stable in the reunion special.

In the trailer for "Part 2" of the reunion, Corey and Messer are seated far apart on the couch. Dr. Drew is mediating as they talk.

Corey asks Messer what her problem is.

"You tell me what the problem is," Messer says to him.

"It's that Miranda gave me a backbone to stand up to your bulls*t, Leah," Corey says, pointing at her. "That's exactly what it is."

"You wanna get started on Miranda?" Messer asks.

"I'm not sure it's fair," Dr. Drew says to Messer. "What's the problem with Miranda?"

Corey tells Dr. Drew that Messer is jealous of Miranda.

"Me and Miranda have a normal, functioning life. She can't keep a husband for more than two years!" he says.

Messer calmly denies being jealous, but then takes a jab at her ex-husband.

"Where were you at your first couple months of marriage," Messer asks, hinting at the time she allegedly slept with Corey after he married Miranda.

"Ok, let's go there," Corey says, increasingly nervous.

He tells her that he's not scared of her anymore.

"You shouldn't have been scared of me from the beginning," she says.

"If I had f*cking done what she done, I wouldn't see my kids!" he tells Dr. Drew.

Dr. Drew asks what Simms is referring to.

Someone in the audience shouts Messer's safe word "monkey" before the argument escalates further.

Simms looks confused.

Dr. Drew explains that the safe word is used when Messer wants to stop strong emotional responses in stressful situations.

Simms says that he's going to start using the word "monkey" too, and the clip ends.

It is unclear from the trailer whether Messer reveals that she and Corey slept together while he and Miranda were newlyweds. Everything will be revealed when the reunion special airs Wednesday, but sources have confirmed Messer made her accusation.

"Leah recently had sex with Corey in the back of his work truck," a source told In Touch Weekly in September. "She was just supposed to meet with him to talk about their daughters, not have sex!"

Miranda was pregnant with the couple's first child together during the alleged affair.

Corey and Messer were married from October 2010 to June 2011. They share twin daughters Ali and Aleeah. Their marriage fell apart after Messer cheated with a former boyfriend named Robbie Kidd.

Later, she married Jeremy Calvert, the father of her daughter Adalynn, whom she has recently divorced.

Watch "Teen Mom 2 Special Reunion Part 2" when it airs on Wednesday, Oct. 7 at 9 p.m. ET on MTV.

Do you think Corey should be kinder to Messer because she's the mother of his children? Should Messer bring up their sexual encounter when he was newly married to Miranda? Share your thoughts in the comment section below.