It seems you've clarified OP that this is more about the lying than the porn use, but of course the lying has understandably led you to question if there are other untruths to be uncovered.
I think that's understandable, but I think what might be happening with you is that all of this is giving you flashbacks to that other awful time when the deceit was so systemic and so undeniably cruel. If you'd gone into this relationship as a fully healed person, or as someone who hadn't suffered such injury, then this incident perhaps wouldn't have assumed the significance and proportions that it has.
I don't think the comments about you wanting to control your partner, or analogies to religion versus atheism are relevant or helpful. As far as I can see, you laid your cards on the table and your H had a choice whether to agree or not to what you said you needed in a relationship i.e. no porn and no lying. He seems to have agreed, but then reneged on both commitments at the same time, without telling you.
I can imagine that you've had a torrid time this past 2 years and for most of your waking time, perhaps you've argued with your rational and hopeful head that what you suspected wasn't true, that your H's lies have been plausible truths and that all the good feelings you've experienced and the actions you saw every day in your H were genuine indications that this man was a good 'un.
Yet your dreams and subconscious told a different story and couldn't be affected by rational thought.
What I suggest you consider is how much of your 'awake self' can be trusted - the good stuff about your H for example. Are your positive feelings about him corroborated by other people in your life, such as friends and family or your older child? Have you ever had reason to think he was lying about other things? Is he someone who is respectful to women and values them? Does he think all women are equal, or does he categorise women into 'good' and 'bad' sorts, especially in terms of their sexual behaviour?
Then think about your 'asleep self'. Are all your images relating to this husband, or does your exH or other people who've hurt you in the past, feature at all? Try to sift out what relates to this husband and this relationship.
It might also help if you rewrite what would have been a 'good outcome' when your husband first went on to a porn site. How would you have felt if your husband had come to you, told you he had been worried about his sexual responses and had tried a porn site to see whether he managed to sustain an erection that way? How would you have reacted, in honesty? Or if he had come to you and explained that he was very worried about ED and wondered whether porn might help? Be honest in your responses and then ask your husband what stopped him being honest. We have all speculated here about why your husband lied - only he can tell you.
If your conversations are circular, a therapist might be able to help but do bear in mind that like any group in society right now, some will be porn users themselves or will have convinced themselves that it is harmless, in order to sustain their own relationships with a porn user.