Assuming what the wife found wasn't left over from before and he forgot about it (here I go again, sounding like I'm defending the dh
) I would make an issue of the lie, if it could conclusively be called a lie. I would highlight the fact that trust and honesty are the building blocks of a relationship. I would ask if he would mind being lied to on a regular basis. One-way truthfulness in a marriage is a recipe for disappointment and disaster.
Perhaps state that since he's doing something like that, which supposedly isn't harming a relationship (in his views), then she is going to pursue some internet or emotional affairs? Surely he won't mind, since "they are not real people." Okay, maybe bad advice, but the analogy may have some merit.
I'm not asking for an answer, but I wonder why he doesn't come to you when he is interested in sex. I'm sure you've told him how it hurts you to see him turn to porn.
I'm sorry I don't have any easy answers. It seems this is a way of life for him since his family thinks it's normal. Is he not a Christian?