You covered a lot in your post and there are many different questions there.
For most men one woman is NOT enough. If this were true the number of cheating husbands would be a lot lower, this is just a fact of our biology. Our genes tell us to fuck early and often with as many as we can get. We might come home to a supermodel wife who is great in bed but we still will start to want others too.
Now some of us get to have our cake and eat it too (thanks Mrs. Ustwo
) but for those who are not porn is a way to get what our genes are screaming for which is variety.
Now this is something you should repeat to yourself.....
Seeing the vaginas and breasts of other women will turn my SO on.
You can't change this HE can't change it, its why he wanted you in the first place. Trying to make him feel guilty and you being hurt will only make the issue worse not better.
You said you went to those sites and were turned on, well rather than making him hide it, go to those sites together. Explore your own desires/fantasys with him rather than trying to keep him from having which is only natural.