I had to throw my 21 year old daughter old out. It was really messy, but sometimes you have to do it---and I know it's hard. Just get yourself some help with the process and remind yourself in every decision you make about him: Is this helping or hindering him growing up? You'll then always do the right thing---even if it hurts you, or you both.
Good luck and no matter what you do, let him make his own life and his own mistakes.