I'm going to present a slightly different view. Everyone so far has given you good advice. Men are visually oriented, however, acceptance is a key.
I was married to someone who very likely became a sex addict. Has been involved with an internet porn queen (literally calls herself a paypal whore), produces porn, and they're relationship is far from healthy. They cheat on each other, set up threesomes and swaps for each other... not really a great relationship. She kicks him out, he bounces around, he finds someone to "care" for him for a bit, she gets needy and calls, he's back there. Strange. I got roped into a few of their cycles. Philosophically, I have no reason to be against porn... free speech, first amendment, and believe in "community standards". However, behaviors can become addictive--"compulsive." It can be an escape or a fantasy. Gambling can be addictive.
Why do you feel he lied? Sure, we all fantasize. Women have beefcake calendars. Lying can be a form of self-protection when we feel intimidated.
He is fearing something. Might be the loss of "opportunity" with other women or may be the weight of a commitment to a marraige.
What you wish to accept is up to you. However, your H is right in one area: you won't find anyone who won't at least fantasize about other women unless they have no sex drive. Acting that out is another problem. Physical attraction is a component that brings us together. But there is more to it afterwards that keeps us together.
Trust is a very personal matter. Trust can be built here by remaining open and receptive to what he is saying. How are other areas of your R? Do you feel able to openly communicate about this issue, if in fact he may be lying out of fear?
On a side note, when I began to notice a real slide in our sex life is about the time I began to discover my ex's problems... depression, involvement in porn, psycho OW (really!). If it's just he's enjoying porn now, without any other problems... depression, inability to communicate, arguments... I don't see any "infidelity."
Too... take a look at the nature of the porn he's looking at. Playboy--tame, almost nothing. But if it's becoming increasingly more risque over time or he becomes more obsessed with it, there is a serious issue. I'm not really a big porn fan. More interested in the real thing if it comes to visual stimuli. But, take another look before you believe you are unable to trust him or that a philosophical infidelity is reason to not be married. Keep posting, let us know what happens.
