Not everyone is as comfortable talking about their porn habits openly, even with a partner. Honestly I think I'd rather lie and say I don't watch any, than discuss with someone what kind of porn I jacked it to yesterday.

Is someone's partner not allowed an ounce of privacy? Does he really have to share his subconscious with you?

Really though, if this elicits the level of reaction from you that it seems it does, then you're right, just leave him. You'd be doing him a favour.