This will open a can I am sure...
I have been in the hobby for the better part of 2 marriages, and now a serious relationship, spanning the last 10 years. I have taken part in the hobby while 1. Married and 2. Single.
As a friend once told me, I love being married, I just don't like the white jacket that comes with it! Seriously though, I think a lot of us are in the hobby for a long period of time for varrying reasons. Myself, I am addicted in the sense that I am forever looking for my Sexual soul mate. I have had many, many great girlfriends/wives/lovers...etc.
It boils down to this: like smoking, MP's and the whole underground scene are habitual. The thrill of who will be behind the door, will we connect, will it be good/bad, what about next time? I could go on, but I think you get the gist of my point. Will I ever be content? I don't know, but I do know that life is short, and I will be damned if I miss out on any of it!