Here, read this
http://www.guardian.co.uk/technology/2011/mar/08/facebook-us-divorces
Now onto you'r little problem. Like crashed said ahe probably added you to a group and just setup privacy settings to the way he wants you to see everything.
This does not mean at all that he is cheating or doing something wrong. The problem here MIGHT(and i stress this MIGHT) be you.... Are you overly protective? Do you question him on every other post he makes to friends, even girls... Do you nag him about what he does.... these type of things are what make even loyal relationships have their set limits. Try thinking all this over and if you still don't get why he did it, question him about it. Their is nothing else you can really do unless you get his pswd and start stalking his accounts....