Is pornography ok in marriage?

I just recently found out that my husband was watching pornography every single day before work. I was hurt. I felt like he wanted other women and that I was ugly cause lets face it, no average woman can compare to thousands of dollars worth of plastic surgery, so I left for 4 days to just clear my mind and think about it. I loved him and decided to talk to him about it, he said he couldnt stop and that it was just something all men do. My relationship before him ended, for many reasons but porn was also one of those reasons. So I find myself in the same boat with my husband now. Is it me? Or is this something all men really do? Should I just leave? Because Im scared that, the expectations in our relationship will change because what happens when porn is no longer enough and he ends up cheating? I just need some help, understanding. I dont want to leave him but he refuses to do anything and its making me feel very insecure with myself. What do I do, should I just let it go? Is it harmless?