Okay, I was just going to pop in and say casts for simple breaks are only on for about 6 weeks, but you found that out.
To kick him out it will depend on your state tenancy laws. In some states you may have to go through the legal eviction process.
However, if he is violent or threatening with you call the police. Once the police are called and there is a police report or arrest you can file for a protective order, which will, essentially, remove him from your home.
I would sit down and think of some rules you need to have peace and comfort in your own home. Curfew? Guests? Rent? Chores? Smoking, Drinking, drug use? Destruction of property? Treatment? Therapy? Employment? School/job training? ...and come up with a contract that addresses these rules.
I understand why you feel bad for him. In part because of your daughter's treatment of him, part because it is hard to let go of the thought of him as a child. Pity isn't helping him and it's torturing you. He isn't a child, and if you think that a typical 19 year old would being is some combination of education/job training/working. He is doing none of that.
If you want him out of the house, set a deadline. Give him whatever time period you feel is reasonable to get his
together and set a date. 3 months, 6 months, a yer, whatever.
Don't feel bad about calling the police about him stealing the car. He was damn lucky. Had it been anyone but you he would have been in jail.
You said your daughter lives with you, too? Where is she in all this? What is her opinion? Her role?