"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...
...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 me 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 go on feeling in a certain way. He might as well promise never to have a headache or always to feel hungry...
...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 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 yoursekf 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. "
C.S. Lewis.