Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...

This has nothing to do with you.
But since this is a problem in your marriage, something has to be done. It doesn't seem he can stop on his own, since he has been looking at porn since I think you said age 12. And before, he said he would stop, then he can't. That is why a professional can help him. Google online for "Sex Addiction". Hopefully you will find some therapists in your city that he can go see.
As long as the categories he was looking at aren't illegal, I mean they have all kinds of categories on porn sites.
This by no means may make you feel any better. I have no doubt that what he is looking at has anything to do with you or that he is looking for something else. If I was to guess, he feels insecure about himself. That has nothing to do with how you and his relationship is either. i'm not saying deal with it, I'm not saying it's right or wrong. That is between him and you. I will say that it's not crazy, unless he is into something really deep that you are not comfortable with. Women physically develop earlier then men, then men become very for a lack of better words "horny and sexual" , then females catch back up around the age of 30 or so. Not sure why, but I do believe it to be true.
But it’s not a multi billion industry for no reason. We are all natural voyeurs to a degree and erotic materials have always existed.
You say he searches for disturbing things. I’m not sure what this means. It may mean the authorities need to be involved at worst. But may just be unpalatable to you at best.
No one can be all things for another. There are things I like to watch that I don’t like to do. There are things I like to do that I’d never watch. Each person expresses their submissive and dominant fantasies differently.
Maybe rather than making things taboo you could explore your fantasies together
My Christian partner and I sat down and agreed at the start of our relationship that even just looking at porn is cheating, neither of us would accept it from the other. However, he hasn't just looked, he has had an addiction. It has hurt our relationship in so many ways. I am not at all a prude, we've done plenty of taboo things together, even some of the things he's searched up on the site. We're both willing to try anything with eachother, and only with eachother. Porn is not only with eachother, that is him seeking something, someone, else to be satisfied with. It's destroyed my confidence, faith in the relationship, and trust in him. Some couples may agree that it's okay to watch, but my partner and I agreed that it wasn't okay and that it was cheating. And he did it anyway, therefore cheating. Porn, cheating, has done nothing but take away from our relationship and he agrees with that.
I didn’t mean to imply anything negative. As you said, it was something you agreed on at the beginning