It's an age-old question every couple faces: Can men and women really be "just friends" or does sexual attraction and jealousy take over? What if one person stays in touch with an ex, or has an opposite-sex pal?
"Good Morning America" special contributor Steve Harvey agrees with Billy Crystal's character in the movie "When Harry Met Sally," who famously said, "Men and women can't be friends ... the sex part always gets in the way."
A study in the Journal of Personality and Social Psychology estimated that an opposite-sex friendship can result in an affair as often as 15 percent of the time.
Who better to weigh in on this classic relationship question than the man whose new relationship book "Act Like A Lady, Think Like A Man" sits at number one on the New York Times Hardcover Advice bestseller list?
Author, comedian, actor and host Steve Harvey tackled this topic with a number of couples.
Justin Vanlandschoot and Stacy Marsch
Married for four years
Vanlandschoot, 33, had a female friend who was coaching him in a speaking competition. Marsch, 37, knew about her, but one day saw an e-mail from her husband to this woman and it was signed, "Love ya."
Although Marsch says that men and women can have opposite-sex friends, she felt uncomfortable and confronted him.
Vanlandschoot says although there was absolutely nothing going on between him and his friend, it was not worth jeopardizing his marriage and he ended the friendship.
"You typed, 'love you'?" Harvey asked Valandschott. "That's pretty dangerous ... I can't even type 'I like you a whole lot' without starting a major fire."
He told Valandschott that he did the right thing by ending the friendship.
"I'm just of the belief that a couple should form a two-handed circle," Harvey said. "Outside relationships ... what good do they bring to your marriage?"
Aaron Bouw and Lindsey Dahlin
Dating for three or four weeks
Dahlin, 25, says it is fine for men and women to "just be friends." However, Bouw, 29, says that women pull the naive card" and don't realize it when a male friend is interested in them. Bouw says he trusts Dahlin, he just doesn't trust her guy friends.
"I know how men think," Bouw said. "We have one thing on our mind."
Harvey told Buow he was trying to mark his territory, not protect Dahlin.
"That's how men are, that's how we really think," Harvey said. "It's almost virtually impossible for a man to be a woman's friend. The only reason we're your friend [is because] you've made it perfectly clear it will go no further than this."
Sharon and Bill Brewser
Sharon Brewster, 53, said she almost called off her wedding because she found a text message from another woman on her husband's cell phone that ended with "sweet dreams."
"I heard Bill's phone go off," she said. "I went out and confronted him. I was very upset."
"She's certainly not saying have sweet dreams about your wife," Harvey said.
Sharon's husband, Bill Brewster, 52, told her that he always got along better with women than men. But knowing that Sharon does not believe men and women can be "just friends," he did not tell her about some of his female friends.
"The big mistake that I made was that she didn't know about her," Bill said.
Mary Fitzgerald and Bill Soldwisch
Dating for 11 years