The Marriage Thing.

"I think you have to keep falling in love with each other," Becca told him, dry eyed and calm. "A man and a woman. A husband and wife. I think that's what you have to do. And if you can't do that, if you can't keep falling in love with each other, then I don't think you've got much of a chance."

Becca in Tony Parson's My Favorite Wife (p. 368)