So like, I wasn’t much better when I was 21, but I do think you did go a bit far here.
It is not your place to ban him or control what he does online, you can however tell him it makes you sad that he watches others. You said as much ypurself and you should probably explain and apologize for the overreach, but explain why. I personally think that watching porn has nothing to do with any partber you may have. It is not a real relationship and possibly even a problem he has, no way to know. What it doesn’t do tho is reflect on you. Finding any other person attractive doesn’t mean he doesn’t find you attractive, there is no correlation.
You should talk it out, without blaming him but explaining that it makes you worried and sad and why, and unless you present it like “he should have known” he will listen if he cares about you. This is not a he problem or a you problem it is a plural you problem (god this sounds better in languages with more exact wording…)
So awesome! That’s what communication does :) if someone is right for you, being honest is always the best way to understand what works for eachother!
Very glad it all worked out. This is how it should feel when you open up to someone that cares about you.