Bella DePaulo, “Singled Out: How Singles Are Stereotyped, Stigmatized, and Ignored, and Still Live Happily Ever After”:

To the new kind of married couple that emerged in the twentieth century, no other feelings seemed as shiny or bright as the love they felt for each other. The fondness married people once nurtured for all sorts of other people who were important to them—well, that now seemed a bit dull in comparison, and maybe not really worth the effort.

Friendships got a demotion. Women still maintained ties with other women, but now they were more likely to enjoy those friendships than to cherish them. The screws were turned even more tightly on the close friendships between men. Those relationships were not just downgraded in importance, they were stigmatized as homosexual and pathological. Bonds with siblings lost some of their luster, too.

Even motherhood took a hit. In Love in America, Francesca Cancian notes that less than a century before the married couple and their feelings for each other had become so glorified, "intimacy and sexual relations between spouses were not central and both spouses had important ties with relatives and friends of their own sex. The key relation was an intense, emotional tie between mothers and children."

But as the decades of the twentieth century ticked by, that was no longer so. For the first time, there was room in the culture for "popular advice books that suggested that having children might weaken a family." Children were still important, and the home that wrapped its arms around Mom, Dad, and the kids continued to be sentimentalized. That bond between husband and wife, though—nothing else compared.