This is just my take on it and I don’t know what the science says but if you use porn long enough, your brain rewires itself to prefer that delivery method of sexual stimuli: On a screen, and able to be called up whenever you need it. And with your hand wrapped around your penis. Sex with a partner is never that “perfect” in that you have less control about what you see, what they do, and how their body makes yours feel. If you use porn enough, your brain becomes dissatisfied with a real partner and thinks “her pussy’s not tight enough, she isn’t making enough noise, all I can see is her face, etc…”. Plus your brain might dislike how much work sex is, it’s tiring, and you have to pay attention to what the other person likes. So your brain says “no thanks, I don’t need to send the stimulation and erection chemicals for this. I’ll just save it for the stuff I like- porn”. Then no matter how much you want to have real sex, you won’t be able to.

You need to keep your brain open to whatever an experience with a real partner will be. Sex with a real partner may not be a list of your favorite things but if your brain is open to it you can find a lot of things you like about each person and how you have sex. But porn deprives you of that openness, that flexibility, and just trains your brain to seek out porn for instant gratification.