I agree with maxmax. Porn is only a problem if it negativly impacts his life, like his and your sex life, financial life, home life (is he ignoring the kids?), etc.
But let's assume it's not an addiction. Maybe he has a high sex drive. That's very different from an addiction. How old is he, how much does he work out, and what are his workouts like (long long)? Working out raises men's sex drives (per my doctor).
So, if you are really worried about him looking at pictures of women that he will never meet, I think it is not he with the problem.
I have a long time interest in psychology, specializing in relationship dynamics for 30 years.
(Please note, we give the best advice we can based on the information given in a post. For better advice, please include the age of all romantic partners.)