Yes I would be upset. To me, feeling pleasure/ being turned on/ sexy photos should be ONLY between the two partners in a relationship. He should be coming to you for his sexual needs, not strangers online. If you ādonāt know how you feel about itā then itās probably a case of you donāt like it, but you donāt know what to do about it. To me, looking at porn, watching porn, looking at/ following/ friending pornstars or OF creators or even just general half naked women then itās not faithful.
It's a type of cheating.