Here is a graph from the National Center for Marriage and Family Research about trends in cohabitation.
More information about Marriage and Cohabitation from Pew Research.
https://www.pewsocialtrends.org/2019/11/06/marriage-and-cohabitation-in-the-u-s/
National Center for Marriage and Family Research : Cohabitation data and reports
https://www.bgsu.edu/ncfmr/resources/data/resources-by-topic/cohabitation.html