I disagree completely; shacking up and actually being married are two VERY different things and can’t show the same results at all.
They’re talking, I think, about the relaxation of the emotional distress of being single. Evidently, for guys, shacking up still feeds single. What’s changed over the years is that women, this drop in stress used to require marriage, but now shacking up does it just as well.
What's the difference? Shack up and one partner can sue for half the assets of the other when they split up in many States...California for one.