The Film: Grady Tripp has writer's block.

He's a college professor with some real problems. One of these problems involves his boss's wife.

The Affair: Grady (Michael Douglas) and Sara (Frances McDormand) appear to be properly in love.

So, although it's deceitful and immoral, it's not so sordid really.  

Long-Term Relationship? Why, yes! Sara falls pregnant with Grady's baby.

Nothing keeps a relationship strong like an accidental pregnancy!