Did you have an agreement that he wouldn't watch porn? If so, then what you really need to be focusing on is the breach of trust, and you need to have a serious discussion about why he didn't feel he could be honest with you.

But if you didn't have an agreement, then I don't think he's done anything bad or unusual. A lot if adults like to watch porn occasionally, and I think it's unfair to automatically assume someone has a problem with it unless it's interfering with their lives in some way. I mean. there's nothing wrong with porn unless it's becoming an addiction of some kind.