Purging is one of the hardest behaviors to break. I have gone a couple of years without doing it and then back to multiple times a day. I understand when you say it is a form of self-punishment, it is often the thought that goes through my head when I am about to do it. I've found that it is just one of those things that the more time in between purges, the less the urge to act on it. It is so hard when you are in the midst of that cycle but it is possible to slow it down and make it a distant memory....hugs