Here's another excerpt from a movie. Shall We Dance is about a husband (Richard Gere) taking ballroom dancing lessons & keeping it a secret from his family. His wife (Susan Surrandon) suspects that he is cheating & hires a private investigator to find out what her husband is really up to. In one meeting the wife had with the P.I., she asks him if he knows the reason why she got married. He guesses, "Love? Companionship?" and some other answers. The quote below is the reason she gave.
We need a witness to our lives. There's a billion people on the planet... I mean, what does any one life really mean? But in marriage, you're promising to care about everything. The good things, the bad things, the terrible things, the mundane things... all of it, all of the time, every day. You're saying, "Your life will not go unnoticed because I will notice it. Your life will not go un-witnessed because I will be your witness."