Is it normal to have off-putting mental images of bf watching porn?

First off, I know porn is normal. Most guys watch it, I know. My boyfriend confessed that until about 3 years ago (before we met) he had a porn addiction. And I mean as in he felt he had to watch it every day, to the point that if he didn't, he would get desperate and sweat. It's something that lasted for years, but he said that at some point he decided to quit and destroyed all the porn CDs he had (he had no internet back then). He had a hard time letting it go, but he did eventually. By the time we started dating, he wasn't into it anymore (or so I think.)

During our first months together, I created a very idealistic image of him, until he confessed about his addiction. I never would've guessed that he had been that type of person. I found it hard to digest and I thought a lot about it, but I finally accepted it as a part of his past (though I must accept my image of him got a little blemish). One day, months after that, when we started becoming more sexually involved, I asked subtly and indirectly whether he watched porn or not. He said he didn't because he didn't need it. I found it hard to believe, but I just went with an "okay" and didn't talk any more about it.

Recently, he's been watching this series, which has been both hailed and criticized for its abundant sexual explicitness. I've asked him about it and he's been honest, saying it really is explicit for TV and that it can indeed be classified as soft porn. He had asked before if I "yes", but then I said I didn't want to, because the pornographic abundance wasn't all that appealing to me (and it never has been) and that it would probably take a lot away from a good plot (which is important to me). We had a conversation about how I think porn and the hypersexualization of women in the media is somewhat degrading(though like I know everyone knows, it's normal for most guys to watch it and love it)and how it makes me feel like I'm not good enough (I know this is silly though). I never explained properly however, the reason why I didn't want to watch the series. It's not so much that I hate the sex scenes as much as I don't like having a mental picture of my boyfriend watching them. It makes my image of him more blemished. I think I would refuse if he asked me to watch the series with him. Though I know that porn-watching is normal, it has nothing to do with me, it's a fantasy, and that it's just something guys use to get off, I can't get rid of the mental pictures. The fact that he's watching the series (even if he's being honest about what's in it) also kind of blemishes my image of him because I feel that what he's interested the most in is the porn (though he would never admit it), and I fear he might go back to his old ways. My question is: Is it normal or is it irrational to be having those ever-present mental pictures and that fear of him reverting? I just don't feel the same anymore around him, and the sexual appeal that being alone with him had before is not just as present.