My wife wrote me last night.. our youngest son, recent HS grad, recent new worker in the real workplace, borrowed her truck to go riding with friends, brought it back on half a tank, and left it muddy... Did not help clean the kitchen after dinner... went to work this morning and forgot to take the garbage out to the curb............Perspective is everything.. My son is 7,856 miles away.......after reading this thread, I really want to give him a hug, tell him to go clean his room, and see if he wants to take a couple of the bikes and ride to Austin and go look at new bikes......then have him wash his moms truck, and go fill the tank..but the email I got this morning said he had already done that, and said he was sorry to his mom for being lazy yesterday,,, was just beat after riding all day...and fell asleep after dinner..Perspective is everything...
I don't have it so bad with my boy after putting it in perspective.
To the OP, sorry for your trouble, no words of wisdom come to me, as I have never dealt with issues like you are now. The only thing that comes to mind is take care of your wife and youngest and never quit.... though for you,, the never quit may be more towards doing what is right for the wife and you. At 18, say good bye to the son, show him the door, and say he is welcome back to the family, but never to the house if things in his life change for the better.
I don't know how I would do that personally with my two sons, but perhaps that is just because when put in prospective they have been nothing but normal kids pushing limits growing, but never really trouble. Other then that time last deployment my Mustang jumped out of the drive way and hit a tree......
Best of luck to you and your son.