kazza,
Please don't be hard on yourself.
Actually you didn't "blow" your diet at all. Your body corrected the inadequate diet you were on. You weren't eating enough. Losing weight is not about starving yourself which is harmful, it is about eating a variety of good and nutritious foods, eating the correct amount (portion), and avoiding foods that are not good for the body.
The drinks lowered your resistance. Your diet was restrictive, punishing, controlling. The drinks you had relaxed you and your need/desire to control through diet.
Please consider seeing a nutritionist, go to Weight Watchers, and/or read about healthy diets and nutrition to learn good habits that will benefit you the rest of your life.
ECHOES