from a man's point. most men are driven quite a bit by sex. with most of us accessing porn at some point. it can I guess become a habit. or addiction.
maybe you should try and look at it together and see if you can see what his turn on is. get him so into you that he's not got enough energy or time to access it. being sexually compatible is an important thing in a relationship

have you tried watching it with him? find out what is his thing, I think that most men have a higher sex drive than women. are you sexually compatible? have him more into you so he has not the energy or time for the porn. this may seem very black/white as it could be a genuine addiction issue?