The holy grail of relationships is more the chase after emotional intimacy than marriage. After all, the economic functions associated with marriage are in decline. We can earn our own keep, have and rear kids when single, and have an estate lawyer handle our affairs as we age.
Unfortunately, the quality of that emotional intimacy is being increasingly eroded by remote (digital) relationships. Instead of physical hanky-panky there are those confidences exchanged, asking and giving advice, joys and sorrows shared in a special way, and the explicit admissions of how much each needs the other.
In The Washington Post, Caitlin Dewey reports:
" ... researchers have recently begun to treat 'remote infidelity' - emotional cheating, via social media or smartphone - as a valid topic of research. And it's on the rise, the noted relationship scholar and anthropology professor Helen Fisher told Salon."
The beauty of emotional intimacy is the sharing of everything - good and bad. Regarding the latter, the couple will someday boast, "We got through that time Joan was suicidal about not making partner at her law firm." They and everyone else know how much stronger that made their relationship.
When there is leakage of the sharing to a third party, it's palpable. Not so much is shared. Intimacy takes a hit. Both parties realize it. The third party tends to bask in having access to the intimacy with so little responsibility.