Hi Lil, and welcome to the SA forum. Your story has a very familiar ring to it. We hear it over and over here on the SA forum. 18 is such a hard age to deal with. They think the are adults and know everything and there is nothing you can do at this point regarding their drug use and life decisions.
Honestly, I think your son sounds like he is going to learn things the hard way. As hard as it will be, I think I would let him go find out how hard life really is without a skill or education never mind while using drugs.
If the car is in your name and you let him take it, you could be held liable if he gets into an accident while drunk or high. So no, he shouldn't get to take the car. I also think you should stop the money altogether . . . he is just using it to buy drugs
He has shown that he does not want a college education. I truly believe that the only help you should give him at this point is if he is in rehab or a halfway house. The college loan money is trickier. If it is in his name, I don't know if you can legally withhold it from him.
Keep posting. You will find incredible help and support here.
~Kathy