A pair of hit shows will deal with contrasting relationship states this fall: impending divorce and lifelong friendship.

What's to come on Brothers & Sisters and The Big Bang Theory? Consider the following storyline tidbits regarding a pair of couples:

• Expect a fourth season twist for Robert and Kitty on the ABC drama, as E! News teases their marriage is tested by both "external and internal forces."
• Over on the CBS sitcom, Penny and Leonard may be bad in bed together, but Jim Parsons says this doesn't mean she'll find love with Sheldon. Ever: "I think that they are so sibling-like. It would be wrong to introduce sex into that relationship."

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.