And, of course, the promise, made when I am in love and because I am in love, to be true to the beloved as long as I live, commits one to being true even if I cease to be in love. A promise must be about things that I can do, about actions: no one can promise to go on feeling in a certain way. He might as well promise never to have a headache or always to feel hungry. But what, it may be asked, is the use of keeping two people together if they are no longer in love? There are several sound, social reasons; to provide a home for their children, to protect the woman (who has probably sacrificed or damaged her own career by getting married) from being dropped whenever the man is tired of her.
—C.S. Lewis, Mere Christianity