This is so hard. I also have only the one child and really, if I didn't have Jabber, I don't know what I'd do. I do know that no matter how much you love someone, you can't let them continually hurt you. You can't let them use you and endanger you...bringing drugs into your house is endangering you. You did everything you could for him...and instead of growing up and being the man you raised him to be he became what he is.
You have to let him find his own way. Someday, he will regret his running through all this money. But he'll be no worse off in the future than if he'd never gotten it at all.
Hugs to you...I wish you, and all of us, peace.