My wife and I have been together for 28 years and yes we are happy together. One of the secrets of getting along is keeping things in prospective.
First thing is men like porn. This fact can be disturbing to women because most women see porn as exploitative and demeaning. It's ironic too because in countries were attitudes are the most Puritanical (like Saudi Arabia) a huge raunchy and vile underground culture of porn develops. As in more sexually open societies such as in the Scandinavian countries, they have almost no real demand for the stuff.
To me porn is like alcohol, an adult pleasure that most people can safely indulge in. Of course you're concerned because like alcohol, porn can lead into serious problems.
Be an adult, tell him what you found and just ask him if you should be concerned about it? And trust him if he says no.
I use to work one man who had his own machine shop. One day his wife walked in and was quite upset over the pictures that were hung on the walls. This was not hard core stuff but more like vintage Playboy.
The wife was very shrill and judgmental. He took it all down but he totally resented it. He saw it as an invasion of his space and his wife as being repressive and controlling. Actually it was something that became a reoccurring theme in their other domestic problems.
Talk to your husband, be open, be honest but don't push him into a corner or make it into a moral issue. Otherwise your husband will feel motivated to lie to you and keep things secret. And that can potenially hurt your marriage far more than smut on the internet because when men feel they need to lie to their wives that's when they start to look for the other woman "who really understands them".