Let him suffer the consequences of his actions. These dental issues are the result of not taking care of his teeth over a period of years. The need for deep cleaning and an extraction are the result of chronic neglect. Let him deal with this. Same with his busted finger. Maybe he'll end up with no teeth and a bum finger. That's his choice. Just like it's his choice to keep pissing his life away with drinking.
You take care of YOU. Which means take your trip, enjoy your cute hair and put one foot in front of the other. And go live.
As to his parents, whether they help him or not, whether they think you're a bitch or not....it's out of your control. You have done your share and now it's time to get off the train.