It is not your responsibility to hold everyone else afloat. Some need to learn to swim on their own and carry their own weight. Maybe you gave him the gift of learning what cost him a good friendship. If he did a drug deal at your christmas party, he was using you as a dropoff point. There is no way he could have not thought at least once how wrong that was or what it could cost you. You did the right thing in that moment, and though it was painful, it was a lesson in what ‘best’ really means.