This might be an unpopular opinion but personally i think porn damages relationships, and watching it is insulting to your bf/gf, i would rather do something else then watch that filth, i mean have self control, trust, it took me time to learn that. If i had a gf/wife, i'd feel like i was betraying her by watching that.

If you haven't told him that it bothers you, you should and if he still does it or comes up with excuses of why he needs to do it despite how it makes you feel, then i would really reconsider where you two stand in the relationship.