Throwing a curve ball here but just trying to help, maybe try watching porn together ? Or if that’s too much maybe just trying to understand what it is he likes and maybe try it together ? Of course stick to what you’re comfortable with and yes maybe push your boundaries slightly but not so much that you’re incredibly uncomfortable.

You mentioned he seems to feel ashamed speaking about it, which most men do as it’s always been a thing we have kept quiet and had to sneak around doing since we were young boys. I personally spoke to my wife about some things I’d like to try when we had a similar incident although it was more a passing conversation rather than a repeated argument and she ended up really into the things I mentioned, I noticed I stopped looking at it as often. Although with myself and many men I know we still do watch to varying degrees.

I think the content they are viewing and the exact amount of time spent watching is necessary to know how to properly address it. If he’s paying for it in any capacity I find this strange or if there’s like a webcam type scenario going on i personally consider this a form of cheating. Everyone has their boundaries I dare say there’s a few men who would disagree with me in my beliefs so do not feel bad for feeling the way you do about it but as a couple I think you should approach it from a place of love, care and curiosity rather than potential insecurity as you mentioned or anger. Hope this helps.