He should have advised you of his porn usage before you married him. He should not have put you in the position of "discovering" it, especially if had reasons to expect that you would react as strongly as you did, and, I imagine, he should have predicted your reaction.

So you should treat the situation as follows: you married someone who withheld critically important information - "critically important" in that with the knowledge of that information you would not have married him in the first place. The appropriate response to this situation is an annulment (rather than divorce). I do not think that my position would find support in current law - in other words, I believe that you may still need to go through the process of divorce- - but I strongly recommend that you adopt this view of what happened in your mind, for your purposes.