https://www.rand.org/pubs/research_reports/RRA2912-1.html
The new analyses found no evidence for a retreat from marriage; in fact, there was evidence for a possible "increase" in marriage resulting from legalization of marriage between same-sex partners
New marriages increased by 1 percent to 2 percent among different-sex couples and about 10 percent overall.
The authors found no consistent evidence for an increase in cohabitation by unmarried different-sex couples or an increase in divorce as a consequence of legalizing marriage for same-sex couples.
Among high school seniors, the authors found no evidence of a negative shift in marriage attitudes, and they found some evidence of an improvement.