Spelling has been married to McDermott, the father of her four children for seven years. The family has starred in several wholesome lifestyle programs on cable television.
However, a woman told UsMagazine.com last month she spent two nights having sex with McDermott in Toronto in early December.
"[Spelling is] much more heartbroken than anyone realized," Spelling's friend told People.
"She's flipping out and is completely devastated. Remember early last year when the tabloids wrote something [about marriage troubles] and she blasted them on her website?" the source said. "Now she's not even doing that."
The source said Spelling doesn't know if she's going to leave her marriage with McDermott over the cheating rumor.
"But no matter what, she's staying strong for her kids. She's all about her family. She worships those kids," the friend said. "I don't know if she's strong enough to leave him right now with everything she's going through and four young kids."