Being in love is a good thing, but it is not the best thing. There are many things below it, but there are also things above it. You cannot make it the basis of a whole life. It is a noble feeling, but it is still a feeling… Knowledge can last, principles can last, habits can last; but feelings come and go… 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 marriage) the grace which both partners ask, and receive, from God… “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.
-CS Lewis