I sympathise, having had partners who used porn. While it not being a make or break issue exactly it did feel cheapening.
I can't help but conclude porn in all its forms is intrinsically damaging. It's largely misogynist but even when it isn't it still turns human sexuality into a cheap commodity. In print porn was at least regulated, but on the Wild West of the internet it has proliferated into dark, twisted and violent representations of sexuality that are increasingly blurring with normal ones - to the point where people potentially lack any concept of normal, healthy sexuality at all.
Plus, there are the concerns women like yourself must have about their partner preffering screen images of porn starlets to their real life partner.
When they are using but furtively like your DP it must be particularly hurtful.
I did use it as a younger man with the advent of the internet, but then read the most shocking book about the porn industry that was the equivalent of one of those documentaries about abattoir practices that put you off eating meet forever. Also, having a daughter changes everything. I now imagine young women not much older than her ensnared in the porn industry.
I am not suggesting everyone who uses porn is being psychosexually corrupted; but some people who do (particularly men) are. In all, if a magic wand could make it all disappear in a flash then the world would be a better place as a result.
Not my business, but if it does make you sick to the stomach you should not stand for it. There is no reason why you should.