"Rumors about cheating have followed them their whole marriage, and it really takes a toll on her," a Spelling friend told People in its latest issue.
"[They] have always been adamant about staying together. I don't think they feel divorce is an option."
The friend added that this is not the first time Spelling has accused McDermott "of having a wandering eye," mainly because the pair spends quite a bit of time apart due to their busy work schedules.
During the weekend of December 7, McDermott was in Toronto as part of a press tour to promote the new reality show Chopped Canada for which he'll serve as host. While away, McDermott allegedly had sex with a woman named Emily Goodhand, who came forward with guilt to reveal the details of their passionate weekend, Us Weekly reported.
"He told me he and Tori had a sexless marriage. I believed him," Goodhand, 28, told Us, adding that they "absolutely" used protection when hooking up.
"He was romantic and very complimentary... I'm sorry. I f-cked up."
While there might be trouble in paradise, a source close to Spelling told People the Tori & Dean stars' marriage may last after all.
"If this story is true, it would be hard for her to admit," said the source.
"She's very dependent on Dean and the whole life they've created together. She's an incredibly loyal person, and she's not someone who gives up easily. Despite their struggles, he's always been her knight in shining armor. And he'll fight hard for her. They'll think very hard before making any decisions about their future as a couple."
McDermott and Spelling have been married for seven years. They met on a movie set in 2005 but both individuals were married to other people at the time. After a three-week affair, they left their spouses and wed in May 2006.
Because of the way Spelling and McDermott's relationship began, the source claimed Spelling's "biggest fear" is that McDermott "would be unfaithful."
In October, however, Spelling defended her marriage, saying it was "pretty damn strong."
The couple has four children together: Liam, 6, Stella, 5, Hattie, 2, and Finn, 15 months. McDermott also has a 15-year-old son Jack from a previous marriage.
Spelling was out to prove her marriage was strong late last year amidst reports the couple was often fighting and in therapy. Spelling had also struggled with life-threatening health issues due to pregnancy complications.
"We have our times when we're not connected, and we have to work at that. We acknowledge those moments and work through them," Spelling told People at the time.