I can't verify this, but it sounds wise enough.
It's certainly been my experience that the majority of relationships that in high school seem like they're going to work nonetheless fall apart within the first couple of years in the real world. Obviously there's a minority that do work out, and not necessarily a small minority either. But getting out into the real world of the job market or going to university can really change a person. Kate and I were in the same place at the end of high school, but her experience in the workforce and my experience in university took us in totally different directions. I became a godless leftie and she got frustrated with my intellectualism and refusal to enter the workforce in favour of focusing on my studies. Obviously that experience has given me some bias here and I think it would be utterly futile of me to even pretend otherwise. But looking at most of the couples I knew in high school, a similar thing has happened with them.
I'd be lying if I said I didn't sometimes miss mid-2005, when we were still in the same place.