((((ReallyHurting))))
I can really empathize with you. I feel very strongly against secretly using porn, despite your discomfort with the idea. I hold very similar beliefs as well, personally. I can imagine how painful this is for you.

We have our reasons for holding such strict policies, as many might think...but as long as we're upfront, and our men agree to our terms, WTH??!
You may want to start off by clearly talking with your hub about this issue again. Remind him of how hurt you feel because he supposedly understood how disturbing the thought was to you (back in 201-). If you are still both looking at the issue like you are now, then I believe seeing a therapist would be helpful for you both. You both need to work on understanding one another's perspective, gain some compassion for the other, and work towards coming to an agreement that you're both comfortable accepting.
Not an easy fix, unfortunately.

But ~ it's not the end of the relationship either. Just a big challenge for you both to work through & make your marriage stronger.
Very best wishes to you, honey. Take care!