Porn and guys go hand in hand. Sorry for the bad pun, but its one of those things that you can never really change about a guy. As long as guys have a functioning hand, they will masturbate. And as long as there is porn, they will watch it. Its in their nature and there isn't much you can do. I say if you can't beat them, join them. Let him watch it. Be the "cool" girlfriend. Cuz really, he's never going to stop watching it so you might as well be cool with it.
Besides, porn isn't about lusting after another girl/person its just a visual aid to help him masturbate. So don't take offense to it. He's just relieving so stress. =)
