****SPOILERS*****At one point the wife very emphatically states that she wants a baby. The couple must have been married for quite a while at that point and that he had been unable to impregnate her. I think that the husband agreeing to let his backward brother to have sex with the wife was perhaps a desperate hope of giving her a baby. But the brother is a premature ejaculator. Disappointment is written in the expression on the wife's face as she urges "Wait! Wait!" Maybe with the near rape by the barman, she saw a vital man who could possibly provide her with a baby. Women who want babies have been known to do some pretty crazy things. There are many psychological disparities about the movie, but if you consider the urge to reproduce as the primary motivation of the wife, it may answer a lot of questions. Very good performances by all. I love being dropped into a time and place totally unlike anything I've ever known and being asked to believe it. All the costuming, environment, and supporting cast helped me to do just that.
Review of The Good Wife
