It's still cheating… bear me out.
Two students waiting for the bus were talking. About their boyfriends.
One said something like, "Well, at least he isn't cheating. They are just facetiming and texting."
It was clear, though, that she was being left out of a lot of a significant part of his day, a part wherein he was having his emotional and social needs met by someone who wasn't his girlfriend. And that…
If the definition of "cheating" is to fulfill wants by means of a person outside of the relationship, then it's still cheating. It might not involve anything physical, but it is still cheating—at an emotional, psychological level.
True in dating and ESPECIALLY in marriage—when things are working as they should be—is the principle that the person with whom you have a relationship needs to be the person you go to have your psycho-social needs met. What does it mean the normal course of the relationship involves only those things outside the psychological—emotional-social domains? It means something is wrong!
If one member of the relationship turns outside of it to have his or her emotional needs meet… Who gets the call when the person is sad? Or angry? Or happy? Who is the first call? If one member of the relationship is looking outside the relationship to have psychological—emotional-social needs met, then the relationship is broken.
Now, there is a slight exception. If there is some context specific thing that is not shared by both members of the relationship, then, naturally, things related to that might be shared with someone outside the relationship. If one member of the relationship is into… origami, let's say… and the other is not, then it would be natural for there to be an origami buddy. BUT, if origami comprises the majority of the person's time and the origami buddy is there for it… Well… it's clear that something is still wrong!
Where does this leave us?
Back to "Well, at least he isn't cheating…"
Yes, he is!
When one member of a romantic relationship is looking beyond the relationship to have wants met, then it is cheating, even if they are only psychological, emotional, or social needs.