From your description what I guess is, he might be having voyeurism. It is one kind of sexual deviation, in which person gets sexual pleasure by viewing woman’s sexual parts, erotic pictures, movies etc. Almost all males are voyeur to some extent but some of them are addicted to it. He is amongst the one who might be addicted. These addicted males keep on watching, collecting and storing pornographic materials in different forms. Many women are very sensitive about men’s habit of looking at pornographic materials and feel neglected. Stop becoming hyper on this but you should leave this topic with a note that you do not like his habit. You have to understand that this is like other habits (Smoking, Alcohol etc.), more you nag more it worsens. Do not think that his habit is because of some inadequacies on your part.