Here is the real question. If you trust him, why are you worried about him looking at other women... either online or offline? Granted, if offline, I'd expect them to be clothed.
The same goes for you. Would you want him getting bent out of shape if you look at another guy?
I'm not saying looking at porn is good. It really isn't. However, if you really trust someone, then you should not have to worry if they look at porn or check out others.
Btw, how did you confront him? Were you understanding and considerate? Or, did you instead start out argumentative and angry?
There's a big difference between:
"I noticed you have been visiting a porn site. Why would you want to look at a porn site?"
"What the **** were you doing looking at porn?!"
How a person responds (including if they lie or not) depends greatly on how you phrase your question.