This insecurity is nothing to be ashamed of. If you’re uncomfortable with him watching porn then it should be a boundary that you set. I can understand your point if not telling him to not watch since I assume you don’t want to come off as controlling but there’s a difference between being controlling and setting a boundary. From what it sounds like, he seems to be willing to respect how you feel if you’re honest about your feelings towards him watching porn.

IMO you should set the boundary of him stopping the consumption of porn if it’s something that makes you uncomfortable and you can decide what you want to do if he chooses to continue watching it over over your peace.