If I could rewind to being 20 years old again I would never make the mistake of keeping a girl around longer than a couple of nights before I'd move on to the next one.
Probably makes me sound like a huge jerk, but it is honestly how I feel.
In no way would I think you or anyone a jerk for making an error in something at least 50% of young marrieds get wrong. We've progressed from simple hunter-gatherer roles to complex lives spent with relative strangers who were often chosen by our hormones. I would have fared poorly marrying young.
About all I did know was that I wasn't marriage material until I sorted out a pretty violent & confusing childhood. Found the right girl but I wasn't close to being ready.
Since alcoholism runs in my family I had perfect attendance at bars from 18 to 50. I also had a chance to test & retest that "grass is greener" theory.
Lots of women but you discover what you need and want is a friend, a partner and someone to hold you. I think you need a good deal of luck to find that early in young adulthood. Heck, I think you're blessed if you ever find it.