:'( :'( Noooooooo!!! Sorry to hear about your fall but don't give up. I'm amazed at your ability to remain clean especially at your age. Your 81 days are a huge accomplishment.
Anyway, try to figure out why you fell, try to make barriers to prevent it from happening again and start over. I'm giving you advice that I didn't follow. I had a clean streak and fell and it took me two months to continue trying. I believe that if you have the strength to continue trying despite the fall, you'll be a bigger hero than if you wouldn't have fallen because now there is less of a motivation to continue (you will not be breaking records for a while). If I were you, I would go out with some friends and reward yourself for your accomplishment (they don't need to know why). Try to focus on the positive and learn from this.
Best of luck!