Porn is just a visual aid to help guys get off easier. They do not care about the plot or acting at all. If you're a woman and you've done a cycle of test you can understand how they feel, they have much stronger urges than women do (for the most part) and then add in if they are on cycle, it can be insane.
Guys jerk off. Guys watch porn. That's all there is to it. They don't really lust the women in the movies, it's just a visual aid as men are more visually stimulated than women are.
Many of them feel guilty or embarrassed about it so they try to hide it. Sometimes it's just their personal space...which everyone is entitled to. Try not to let it get to ya. His watching porn has nothing to do with your relationship.