I couldn't answer exactly, but one guess would be that there is more turnover in relationships at very large universities. In high school you largely move throu

I couldn't answer exactly, but one guess would be that there is more turnover in relationships at very large universities. In high school you largely move through the same classes with the same people in the same grade, versus college where you initially take a bunch of gen ed classes with people whom you may never even run into on campus again, and with more intermixing among a larger population. Also that you're younger in high school, so the time spent there is a greater fraction of your life up to that point, making the experience seem longer overall. A year or two at high school age can seem like an eternity, where as a year or two in your late teens or earlier twenties is a smaller drop in the bucket. Hopefully not just my perception - many seem to acknowledge that time seems to go by faster as you get older. Plus many people go to college, at least the large state schools, with no real intention of actually finishing. Fewer people have that attitude towards high school. Both people can try to build a long lasting friendship, but if only one is trying while the other is being opportunistic, it's less likely to go anywhere (speaking generously).