If you can't be certain that you'll win, don't play the game. You've got too much to lose this time.
If it walks like a duck, quacks like a duck, and looks like a duck, it's probably a duck. You've been giving someone too much benefit of the doubt and letting them get away with things for far too long. If they have shown you, time and time again, that they can't change their ways after being given so many chances, you may need to consider taking more drastic action. You can't carry them any longer if they're not willing to pull their own weight and take responsibility for themselves. If you've offered strategic help and they have not progressed or made an effort, it's time to re-evaluate; either put them on notice or move on.
When you delegate, make sure that you know exactly what you are delegating and what you want the outcome to be.