Apparently, couples who separate — but don't divorce — are a common modern phenomenon.Omaha Sage Warren Buffett, Jann Wemmer, and Willem de Kooning all fall into this "It's Complicated" category.. [NYT]
My dad has lived in Japan for the past 10 years. He use to come visit about half a dozen times but now he comes back to the States twice a year and my mom goes to Japan once a year usually. They are pretty much separated but neither of them felt the urge to get a divorce.
Now my mom is finally wanting to move on so they are slowly starting to separate their finances and so forth. I have a friend who thinks this is very dysfunctional but I think they are going to have a very civil divorce when it finally happens. If they had done it the few years after my dad's infidelity I think it would have been very contentious. Different paths work for different people.