Trying to be ok with porn in my relationship

I've been in a relationship with my boyfriend for two years now. I found out a year ago he watches porn. Ever since I found out about the porn I've done a lot of reading on how best to deal with it. Porn in a relationship is something I cannot understand. For me it has no place. And in order for me to try be ok with something I have to understand it. I have even tried to watch porn myself and I can understand how it is arousing but it's still not something I would actively go search for myself. It's not just porn it's also looking up pictures of naked girls. He searches for pictures and porn 2-3 times a week and when he does search it he spends about 30 minutes to an hour doing so. We have a great relationship in every sense and a great sex life. This is literally the only thing that we don't see eye to eye on and it's getting to the point where it's killing me. He knows how much it hurts me but still carries on saying it's just silly insecurities of mine and it's normal, that all guys do it (as with a lot of the articles on the Internet). Firstly, I've grown tired of the notion that's it's normal. It really bugs me that we have been conditioned to believe that this is totally acceptable behavior in a relationship. Something that women must just accept. Secondly, while there may be an insecurity here and there, for me it goes deeper than that. For me a relationship is physical, emotional and mental - when he is watching porn at that moment it's all about his desire regarding the object he is watching. It's him imagining having sex with someone else. And while it's not physically cheating, for me it is cheating on some level.

Its getting to a point where it's messing up our relationship and I don't want to end a good relationship on every other level over something so stupid that we cannot see eye to eye on. But at the same time I also realise I can't stay in a relationship feeling like this and just pretending it's ok. maybe there is another way to look at this that I am missing - that I haven't read or thought of? I just want to get over this shitty issue in one way or another.