I dated a girl for 4 years, starting the second half of my junior year of high-school. The girl you knew in high-school will probably not be the same girl 2-3 years from now. In the scheme of things, 1 year is not very much time... you WILL fight, both of you WILL change. It's inevitable. That doesn't mean you won't make it--but the way you feel now about your relationship will change. Not to say it's impossible, but a lot of those people that were high-school sweethearts were as determined as you were at making things work--I'm one of them. Just be open and honest with your girlfriend about everything you can, especially the direction you decide you want to take with a career, because her idea of what she would like could be completely different than what you want to do.
You're right but we've changed already. We went into it with no commitments. Just best friends even. We never expected to get so close. HSC (final exams in high school in Australia) kind of brought us closer I guess. What happens when uni starts is anyone's guess.