From A Year With C.S. Lewis:
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 realizing that, when they have changed, the glamour will presently go out of the new love just as it went out of the old one. In this department of life, as in every other, thrills come at the beginning and do not last. The sort of thrill a boy has at the first idea of flying will not go on when he has joined the R.A.F. and is really learning to fly. The thrill you feel on first seeing some delightful place dies away when you really go to live there…
Another notion we get from novels and plays is that ‘falling in love’ is something quite irresistible; something that just happens to one, like measles. And because they believe this, some married people throw up the sponge and give in when they find themselves attracted by a new acquaintance. But I am inclined to think that these irresistible passions are much rarer in real life than in books, at any rate when one is grown up. When we meet someone beautiful and clever and sympathetic, of course we ought, in one sense, to admire and love these good qualities. But is it not very largely in our own choice whether this love shall, or shall not, turn into what we call ‘being in love’? No doubt, if our minds are full of novels and plays and sentimental songs, and our bodies full of alcohol, we shall turn any love we feel into that kind of love: just as if you have a rut in your path all the rainwater will run into that rut, and if you wear blue spectacles everything you see will turn blue. But that will be our own fault.
–from Mere Christianity.