'Emotional affair' could be as harmful to a marriage as an extra-marital sexual relationship, say experts.
Even in the absence of physical intimacy, the constant emotional and psychological involvement with another person can siphon off feelings of commitment, contentment and closeness that two partners previously shared.
"As emotional intimacy develops, you're no longer connected to your partner," the New York Daily News quoted Lauren Mackler, relationship expert and author of 'Solemate: Master the Art of Aloneness and Tranform Your life.'
"Your focus and energy on your partner are dissipated and redirected to someone else. Emotional affairs cause many relationships to die," said Mackler.
An emotional affair can start innocuously enough, said New York City couples therapist Irina Firstein, as an intense friendship that over time intensifies.
"Before you know it, you are confiding in someone else other than your spouse.
"It's a betrayal," she said.
Mackler said: "When you don't tell your husband when you have lunch with the person, that's a signal something is not right.
Not all close friendships are marriage wreckers, and many happily married couples have activities and hobbies of their own, say experts.
"They may belong to a bike club or a tennis club, and if it stays within that activity, it's not harmful," said Edward Schechtman, a psychologist.
"But the boundaries blur when you start talking about personal issues outside of the activity. That's when you start running into trouble," said Schechtman.