Relationships and porn

So last week I was on my boyfriends phone. Not snooping just playing on it. And I went to go on the internet and it popped up that he was watching porn. This entire week he was very secretive about his internet browser and we were getting more and more distant. It didn't click why it bothered me that he was watching porn. I didn't care if he saw it or watched it. It did bother me that he lied about it. But there was something else that I could just not think of. I just now realized it's because it can make him have expectations and make him less attracted to me. We were having great sex before and then when he started watching it again it pushed us a bit father apart. It made us feel like we were loosing something. Does anyone else feel the same way if your SO watches porn?