"My worst nightmare is what I did. Absolutely, I cheated on my wife," he tells the therapist as his wife looks on.
"Or that you got caught?" Spelling, 40, interrupts. After a long pause and a heavy sigh, the Chopped Canada host, 47, admits, "I don't know."
Back in late December 2013, Us Weekly broke the story that the father of four had an affair with 28-year-old Emily Goodhand. In the April 28 cover story, Spelling opened up to Us about her own traumatic experience with discovering the affair.
"He was very nervous -- I saw it in his face," she told Us of confronting her husband of 8 years. "He said that they had kissed but that was it. I knew in that moment the worst had happened."
In True Tori, McDermott talks about his disappointments when it came to the couple's sex life.
"We had sex once every two weeks. It wasn't fantastic," he told the therapist.
"I can never give him enough sex!" Spelling replied. "He's never going to be happy with just me."
McDermott, who entered treatment for an undisclosed addiction following the news of his affair, claims there were no emotional ties to his infidelity.
"I wasn't attracted to her. It was just like a warm body," he said of Goodhand. "Sex was an escape, just like drugs and alcohol."
Watch the clip above! Lifetime's True Tori premieres Tuesday, April 23 at 10 p.m. ET.; Pick up the latest issue of Us Weekly for Tori Spelling's first interview since the scandal broke.