This mama knows how hard all this is for you and you and your boy are in my prayers.
That said, I need to make two points here...one is that as long as he lives under your roof, you are in danger of being stolen from. The possibility has already shown itself and one day you won't catch him in time or the urge will be greater than any threat. This happened to me, I pray it doesn't happen to you.
The second is that when his "departure date" arrives, don't be surprised if he is still there because "he had nowhere else to go" and will tell you all about living under a bridge or dying on the street. Prepare for this, it may not happen but it is often how it works. When this happened to me, I handed my son bus fare (city bus not out of town) and phone numbers of a shelter, a detox and a meeting list. The choice was up to him...go somewhere for help, or go somewhere for drugs. Whatever he chose at that point had nothing to do with me putting him out.
Good luck with this, I hate sounding negative but preparing for very real possibilities may help you keep your sanity.
Hugs