Hi Heart, Welcome to LS!
You'll find lots of people on here in a similar situation to you so don't worry, theres plenty of help and advice at hand
"Out of the blue" breakups are one of the worst kind (i know - i'm trying to cope with one right now). One of the hardest obstacles is that your 'coming to terms' has only just begun, where as he will have been considering it for some time. You should be considerate of this fact in your healing, as it will greatly help you.
Your first course of action should be NC which means NO CONTACT. Contact is not just defined as talking to him, but also covers emails, texts, reading his myspace, looking at photos etc etc. In order to either heal or bring him back, you need to stop all contact.
The primary objective of NC is to heal yourself. To help you come to terms with your own feelings, wants and needs, without any other distractions. Its hard, I know, trust me.
Im sorry to tell you this, but as you said it was a first love relationship, and youre both pretty young. He probably just wants to go off and experience the single life, if he hasnt already got someone else. I know thats not what you want to hear, but the sooner you accept it the better, trust me. Im in exactly the same position. Putting thoughts off, avoiding emotions and locking things away in your head is the worst thing you can do, at this early stage anyway.
The only point at which you should allow a breach of the NC is if he contacts you, saying exactly what needs to be said. Anything else is him fishing for an ego boost.
If you want him back, you need to be the person he fell for, or better. Being a miserable, broken down shell of the person you used to be isnt going to make him want to come back. Get yourself down the gym, get fit, buy some new clothes. Do things for yourself to make YOU feel good. Keep yourself busy most importantly.
Hang in there. Just remember, if you feel yourself weakening to contact, post on here first and we will whip you into shape!
Rocket