The truth is that adolescence is just one long goodbye. You will slowly learn to give your son responsibility, and he will learn to take it.
There isn't a light switch that goes off at the age of eighteen or when your son graduates from college that pronounces him ready to be an adult. Teens need to be groomed for the real world from an early age. They need to be given small doses of responsibility. Think of these as test doses.
You may find you have a few more fights with your son in the months between high school graduation and the start of college, particularly over issues like curfew. Try to deal with this argument before it becomes an issue.
Since the process will take years to master, you have lots of time to teach your son, though toward the end you may feel a sense of panic that your son isn't quite ready.
Try to remember that the time you have left is precious but limited. Consider writing out a list of the things you have left to teach him. Share that list with your son. Let him have a go at making suggestions about what he wants to learn, either on his list or on yours. Remember, just because he goes off to college doesn't mean he can't ever come back.
As you let go, you may feel like you're leaving your baby to be devoured by wolves. That is not the case. You have spent the last thirteen-plus years working hard to teach your son things that will help him be a self-reliant and good person.
A study by the National Center on Addiction and Substance Abuse shows that in a house that has established rules, teens were less likely to drink or do drugs. Teens also reported better relationships with their parents.
You have built your son's character and taught him the skills he needs to think and live. Now it's time to take a step back and let him go. This means having confidence in yourself as a parent and trusting the work you've been doing for all those years. If you let him go, he will fly as you taught him to do.