I'm really sorry you are going through this, it just really really stinks.
I think the worst part about the computer porn thing is he is acting like a child who got busted. I mean, what grown man actually thinks he's going to get away with THAT lie? It's not like you have a 14 year old son to blame it on or something.
My husband has been known to watch a porn or 2 in his life, and it really doesn't affect me one way or another -- heck, I've watched it with him (a long time ago, not really my thing
). The thing I would just absolutely NOT be able to tolerate is that lying. How on Earth could you ever trust one single thing out of his mouth if he is looking you in the eye and swearing he didn't do something that you have proof of? Despicable, really, and a deal breaker for me.
I don't have much advice for where to go from here. I think it would fully depend for me on his agreeing to go to some kind of counseling - alone or together. They don't do miracles in counseling, but if he were willing, at least it would show that he gives some kind of a care about your feelings. EDIT, I was posting when you were talking about the counseling. Maybe it's time to go back, you should have quite a bit to talk about now.
I'm sorry.