Don't do what I did...I had a long term relationship in high school that went into my freshmen year of college...and after that break up I kinda just moped around for a year after that breakup. At the time I was never one who took failure and rejection very well, and after a failure with an attempt with some girl happened, I basically backed off and wouldn't do shit with anyone. In general, I've always been someone who would rather be in a relationship than just a casual fling or what not. However, later on I did have a few flings that I thought might have relationship potential, but they went no where (bullshit drama was usually involved).
I had a relationship earlier this year that only lasted a month as the girl and I were better off being friends than in a relationship (We became much closer as friends, and no, there are no benefits involved).
At 23, nearing 24, living with my parents and done with school, it's hard to meet for me to meet many new people. So at 18, unless you live on your computer all day, its not going to be that hard to meet new people. IF you're going to go to college, there are plenty of people to meet. So go out and have fun. Something I wish I did more of from 18-21...but whatever. Nothing I can do about that now, just have to make the most of the future.