Over the last four decades, many Americans have moved away from identifying with an “institutional” model of marriage, which seeks to integrate sex, parenthood, economic cooperation, and emotional intimacy in a permanent union. This model has been overwritten by the “soul mate” model, which sees marriage as primarily a couple-centered vehicle for personal growth, emotional intimacy, and shared consumption that depends for its survival on the happiness of both spouses. Thus where marriage used to serve as the gateway to responsible adulthood, it has come to be increasingly seen as a capstone of sorts that signals couples have arrived, both financially and emotionally—or are on the cusp of arriving.
National Marriage Project, qtd. by Ross Douthat in “Culture, Class and the Decline of Marriage”