This post is a list of other posts that go into some detail about research and trends on cohabitation. There are many more but this is a solid list as a jumping off place.
A 2018 post on trends in cohabitation based on new data from the CDC released at that time.
An overview of the inertia hypothesis and why living together before marriage may not provide the benefits that most people expect.
A post reviewing the inertia theory with scores of links related to the idea that cohabitation increases inertia, which, for some couples, makes it harder to leave before they had worked out a commitment to the future together.
A fun, engaging video from the team at PREP on inertia.
On YouTube: Relationship DUI
Two articles on the research by Rosenfeld and Roesler that shook up the assumption that cohabitation before marriage no longer leads to increased risk in marriage.
Motivated Ambiguity: Is this a date or not?
Weak and Strong Links: Asymmetrical Commitment in Unmarried Relationships
Links to papers and articles related to asymmetrical commitment
You can lower your risk of divorce. Advice to singles
Searching for "The One": Mate Selection in this Modern World
Attachment and the Perfect Storm. A piece speculating about the difficulties for forming attachment in an ambiguous relationship world.