How do you know he is watching porn 5 minutes after you leave the house if he is lying about it?
Anyway, I personally don't watch porn and think it is wrong to do so. That being the case, I'm probably not the best one to answer or give you advice. But I will anyway. Find someone who values you more than he values porn, or sex for that matter.
But again, that is my personal view based in large part on my personal morality. I think porn is harmful to a couple's relationship for a number of reasons. Others will soon be on here to tell you there is nothing wrong with what he is doing and you shouldn't worry about it. In the end, you have to decide what you are willing or not willing to put up with in the relationship.