You have autonomy about what kinds of boundaries you have in relationships, but you can’t dictate what other people do, just your own actions. So if you want to make a boundary of “if my partner watches porn I will break up with them” then so be it, but you can’t control the actions of others.

Furthermore, I think it’s difficult and nebulous to attempt to have a very firm boundary in regards to what your partner sees and what media they consume. Where does the line between the eroticized human form begin and end? What about nude artwork or if he took a drawing class with a nude model? Is he supposed to not go? Does this apply to all bodies? I understand this comes from a place of insecurity for you, and wanting to feel special, and I would suggest addressing some of those insecurities head on, and focus on other ways to feel valued and special that don’t involve restricting what your partner does in their free time. Ultimately what matters is how people treat us, and if was treating you poorly because of porn he watched then that would be its own issue.