You’re right, there’s a big difference by class. For upper and middle classes, living together has become one more step in assuring the couple will do well if/when they consummate the marriage, at which point there’s a high likelihood of them staying together, at least until the kids are raised.
For the lower classes it tends to be part of a revolving door lifestyle, whether or not dictated by government benefits.
It’s not surprising that the “lower classes” suffer from low IQs. On average they don’t think well, have very short time horizons, and are acutely emotionally immature.
Or am I describing politicians?