"Should we live together first?" Yes, say Democrats. No, say Republicans (even young ones) (Richard V. Reeves, Nathan Joo, Brookings)

There is a marriage gap in America. This is not just a gap in choices and actions, but in norms and attitudes. Each generation is more liberal, on average, when it comes to issues like premarital relationships, same-sex marriage, and divorce. But generational averages can obscure other divides, including ideology—which in many cases is a more powerful factor

http://www.brookings.edu/blogs/social-mobility-memos/posts/2016/05/19-cohabitation-before-marriage-democrats-versus-republicans-reeves