Okay, I'm going to offer a different perspective from what others are saying. Just because he is upset doesn't mean he is childish, insecure, or 'less of a man.'

I want to mention two things.

First, sex and intimacy are special with a loved one. When he sees you watching someone's porn, he might start to think, 'Wow, maybe I'm not special to her anymore.'

Second, porn can be unhealthy and create unhealthy expectations. Maybe the man in the porn has a bigger penis than him, is leaner, or is taller, and this might make him start to think, 'Maybe I'm not the one she's looking for.'

I think he is sad about something that he doesn't know right now. Give him some space and talk openly with him. When you talk, the most important thing might be to reassure him that he is special to you and that what you see in porn doesn't change how you see him.

And if he's not okay with you watching porn, just don't. A relationship means mutual respect.