Coming in late, but had a daughter who used. We didn't know how much or what, but we bought her a used car before we were aware she was REALLY into drugs. It was good that you sold your son's car. My daughter had an accident with her car. Then she conned her straight arrow brother into buying her another car ( I warned him) and she destroyed that one too. After we made her leave, she was driving somebody else's car in Illinois and had a really bad accident that was her fault. She ended up owing the driver $15,000 as she was sued. Way after she was clean, she still had to pay her father back every month. He paid for it, but insisted she pay him back and, after she got clean, she was a different person and actually did pay him back. But going back to difficult child's who drink, smoke pot, use harder drugs, does it matter...?....they are not safe drivers and in my opinion it's our responsibility to do all we can to keep them out of a car. We may not be able to do it, but we have to try. After the third accident, Daughter found herself living with straight brother who would have thrown her out if she even smoked a cigarette in his house and she walked back and forth to work. She learned a lot about responsibility there.
It is never a good idea to bail out a difficult child. They think you'll always do it, and they take advantage. Then the first time you don't, they hate you and let you know it. in my opinion it's actually better to let them sink, then have to find a way to swim.
(((Hugs))) and you did the right thing!