I wasn’t trying to find it....

So I have been waiting for my boyfriend to propose to me for a long time now and so I was looking through his history to see if he was looking at rings to get me. Well instead of finding pages of beautiful engagement rings I found a bunch of porn. I have expressed to him that him doing this bothers me. And before you start telling me that I shouldn’t be mad about it, I’m not self conscious or that shit. I just believe that if your in a sexually committed relationship you only think about your SO not porn. So I confronted him about it and he admitted to it and I instantly broke into tears and freaked out. Eventually I told him I forgave him but lately I can’t stop thinking about it and wondering if he’s watching it again. We have been together for 3 years and I have always trusted him with all my heart and after this I feel broken and hurt. What do I do? How do I move on? I want to stay with him and I still love him but I don’t trust him.