nothing went wrong. she grew up.
being apart lets you realize alot of things about yourself, especially when you're off to college for the first time and taking in alot of new things at once.
not to pee in your wheaties, but high school relationships rarely work out. sometimes they do, but usually not.
6 months is relatively short also. i had a 2 year deal going with a girl from high school that lasted right up until she graduated. suprise suprise, she grew up too.
hopefully it works out the way you want it to. if not, trust me. you'll look back on it in a year and wonder why you got all worked up.