The actress said she was wed to actor Parker Stevenson and Swayze to dancer Lisa Niemi when they began an intense emotional -- but non-physical -- relationship while making the 1985 Civil War TV miniseries "North and South."
Alley told "ET" she and her co-star attempted to avoid "going down that road," but fell in love anyway.
"Both of us were married," Alley said, adding they did not "have an affair."
"I think what we did was worse," she said. "Because I think when you fall in love with someone when you're married, you jeopardize your own marriage and their marriage. It's doubly bad."
Swayze was still married to Niemi when he died of cancer in 2009.
Alley divorced Stevenson in 1997.
J.J. ABRAMS: The Producers Guild of America said Monday it plans to honor J.J. Abrams with its 2013 Norman Lear Award for Television.
The distinction will be bestowed on the 46-year-old writer-producer-director at the 24th annual PGA Awards Jan. 26.
Best known for his work on the TV shows "Felicity," "Alias" and "Lost," Abrams is the founder and president of the Bad Robot production company, which he runs with his producing partner Bryan Burk. The company's current series are "Fringe," "Person of Interest" and "Revolution." Abrams' film credits include "Mission: Impossible 3," "Star Trek" and "Super 8."
"J.J. Abrams has produced some of the most iconic and highest-rated television shows of the past decade and longer, series that have changed the landscape of television," Producers Guild Awards chair Michael DeLuca said in a statement.
"His talent is astonishing, and through his commitment to ingenious storytelling, compelling characters and television programming of the highest quality, he truly lives up to this award's namesake."
"It is an incredible honor to be asked to accept the Producers Guild Norman Lear Award, especially since Mr. Lear is one of my true heroes," said Abrams. "I feel privileged to be included among the prestigious list of past recipients, and look forward to celebrating the work of my fellow producers in January."
Cusack's film include "The Raven," "Grace is Gone," "America's Sweethearts," "Being John Malkovich," "Con Air," "Grosse Pointe Blank" and "Say Anything."
"New Crime Productions and John Cusack are currently considering a project about the larger-than-life radio personality, Rush Limbaugh," a representative for Cusack's New Crime production company told The Hollywood Reporter in a statement. "Betty Thomas, who covered similar terrain in ['Private Parts,'] her portrait of Howard Stern, is interested in directing. The script would explore the rise and reinvention of American Talk Radio, and Limbaugh's continued influence and impact over the last three decades in that world."
MICHAEL BUBLE: Canadian crooner Michael Buble says he has taped a Christmas special for NBC in his native Vancouver.
"I'm so excited to be back on NBC for another big Christmas special which we got to tape in my hometown of Vancouver," Buble said in a statement Monday. "We had great fun with our guests and I think the show really captures the joyous spirit of the holidays."
Buble also starred in a holiday special for NBC last year.