My personal opinion???
STAY OUT OF IT!!!!!!!
Do not be a 'surety' for him. You might suggest (only if he asks) he try something for himself, an addiction counselor, Narcotics Anonymous (NA) or Alcoholics Anonymous (AA) if he feels he may be developing a substance problem, or NarAnon or AlAnon as one having a friend and/or family member that is addicted or alcoholic. Many attend AlAnon, only because usually there are many more meetings of AlAnon than NarAnon.
You have put yourself in a very precarious position, and it may be time to just start worrying about yourself. You really cannot help anyone but yourself.
J M H O
Love and hugs,