It isn't until he meets his son's future in-laws that he realizes he is tired of a three speed life. Time to move up.
When Donald Roth was a kid in the late 60's on the South Side of Chicago, he had a Schwinn Sting Ray bike. Everyone did. But everyone else had a five speed. Donald's was a three speed. It was good enough, as was explained by his parents, just as their Ford Maverick wasn't the neighbor's Le Mans, but it was good enough. And that's the way Donald was taught to live his life. It was a three speed life. It was good enough.
He marries Emily because she's good enough. Emily marries Donald because that's what she had planned, and she is not going to experience divorce as did her parents. Donald opens a law practice with his two best friends and roommates from college because it's good enough.
Then the Roths meet their son's future in-laws and everything changes.
Donald wonders if, in fact, he could get that five speed.
Everything is perception, to be a soul-mate doesn't always happen first time around, and illicit affairs are not always one-sided.