Well, if he is underage, then the only thing you can do to keep him from "running away" is turn him over to the authorities. If he wants to get away from you, he will. You can't stand there watching him 24/7. I dont' know what the age of consent is there, but here it is 17 (means they can move out, get married, etc.)
Take a deep breath and be prepared to let go and let nature take it's course. It is the only way you will stay sane in the long run.
I highly recommend you read "Codependent No More".