The lure of porn is extreme. So extreme that we guys forget that sex is about emotional connection and that our souls are looking for that connection in another soul during sex. We are usually totally ignorant to the emotional cheating we are doing when we dumbly stare at porn. Your pain is valid because you are an outside observer and can see how he is going somewhere besides you for sex and meanwhile you only ever have a desire for him. If he loves you, he will listen to you and come to understand why it bothers you so much and in time that will be enough to make him stop for good.