Oh I have gone through this too, many a time.
Check out the forums on http://www.fitnessthroughfasting.com
in particular look for comments from tinajfreeman and Chimp, they are so encouraging. They explain why we want to eat. I find their thoughts on what makes a successful fast particularly helpful and insightful. They practice intermittent fasting instead of straight fasting for a set period. They also make it acceptable to break a fast and explain its all part of the big picture when your aim is a change for life.

Feel good about yourself!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
(aha that's what ausijuisfast commented to me when I was beating myself up... I am passing the good word around....)