I don't have much to offer as far as Moiraine's specific questions because I'm not in a relationship, but I think a better question is how many guys look at porn privately while being in a relationship? And whether or not that is healthy and/or respectful.
It's an interesting animal. I'm with knapp in that professional pornography just doesn't do anything for me, because it's so far removed from any reality or even any pleasant fantasy for me. Not to mention the porn industry is all kinds of dark and twisted, and the studies of effects it has on the brain and on correlation with ED are pretty concerning.