While I agree that it
can be a form of infidelity, it isn't always.
I think that viewing porn is fine, until it reaches the point of obsession. Some can manage it, others can't. Others find it a temporary obsession and are able to move on once they see their reality.
The article mentions
Second Life and similar sites. While I was still married, I had an online sexual relationship through one of these sies because I needed the validation and wasn't willing to admit the marriage was failing fast. Somehow my husband had found out (or maybe I told him, I truly don't remember) and confronted me and I recall defending my actions, saying it wasn't cheating. It did hurt him. Looking back now, I can see that it had become an obsession and was cheating. My intent was self-gratification, body and soul, because I wasn't getting it from my marriage.
Although I still view porn sometimes, most of those times are with the man I love. I'm no longer obsessed. At least for now.
Sometimes it is, sometimes it isn't.