My thought is that you can't make your co-worker change and you can't control your boss's response to it. I know that it bothers you, but you really have to let it go. You need to keep focused on your recovery and not let this get in the way.
What is going to happen will happen. If it is affecting your ability to get your job done, you must report this, but not from an alcoholism perspective, but rather from a "the work isn't getting done because employee-name isn't here or isn't delivering". Your boss is enabling, but that is his right - if he wants to spend the money.
Just my thought.