Please explain why porn is cheating

Because I hear this argument a lot. It's not only an argument, it's the symptom of porn being so normalized , even in relationships

"porn isn't cheating, especially if there's no OF involved or cam girls or chatting with other women because that would be definitely emotional cheating."

But when they say, that it's not cheating (because they don't chat with other women, """just""" watch PornHub, for the ""fantasy "" , just to get off) how would you argument that it is cheating indeed because it freaking feels like it. Lusting after other women, (also when the women are replaceable..it doesn't make it better)