C.S. Lewis on Marriage

the following quotes are from C.S. Lewis' Mere Christianity  

On Union and Divorce. The Christian idea of marriage is based on Christ’s words that a man and wife are to be regarded as a single organism—for that is what the words ‘one flesh’ would be in modern English. And the Christians believe that when He said this He was not expressing a sentiment but stating a fact—just as one is stating a fact when one says that a lock and its key are one mechanism, or that a violin and a bow are one musical instrument. The inventor of the human machine was telling us that its two halves, the male and the female, were made to be combined together in pairs, not simply on the sexual level, but totally combined... [Thus Christians] all regard divorce as something like cutting up a living body, as a kind of surgical operation. Some of them think the operation so violent that it cannot be done at all; others admit it as a desperate remedy in extreme cases. They are all agreed that it is more like having both your legs cut off than it is like dissolving a business partnership or even deserting a regiment.

On Being 'In Love.' The idea that ‘being in love’ is the only reason for remaining married really leaves no room for marriage as a contract or promise at all. If love is the whole thing, then the promise can add nothing; and if it adds nothing, then it should not be made... [No] feeling can be relied on to last in its full intensity, or even to last at all. Knowledge can last, principles can last, habits can last; but feelings come and go. And in fact, whatever people say, the state called ‘being in love’ usually does not last... Who could bear to live in that excitement for even five years? What would become of your work, your appetite, your sleep, your friendships?

In Love versus Loving. But, of course, ceasing to be ‘in love’ need not mean ceasing to love. Love in this second sense—love as distinct from ‘being in love’—is not merely a feeling. It is a deep unity, maintained by the will and deliberately strengthened by habit; reinforced by (in Christian marriages) the grace which both partners ask, and receive, from God. They can have this love for each other even at those moments when they do not like each other; as you love yourself even when you do not like yourself. They can retain this love even when each would easily, if they allowed themselves, be ‘in love’ with someone else. ‘Being in love’ first moved them to promise fidelity: this quieter love enables them to keep the promise. It is on this love that the engine of marriage is run: being in love was the explosion that started it.

The Ephemeral Nature of Moonstruck Love. People get from books the idea that if you have married the right person you may expect to go on ‘being in love’ for ever. As a result, when they find they are not, they think this proves they have made a mistake and are entitled to a change—not realising that, when they have changed, the glamour will presently go out of the new love just as it went out of the old one.