bulimia isn't just about the food. it's a mental/emotional problem. you can get to a point, even if you're skinny, where you don't feel complete without it, thus, there might be something lacking in a different area of your life. the thought of "i can throw this up easily and not have to worry" can get to a point where you aren't able to control your eating habits anymore, or its extremely hard.
idk what you can do besides tell her you love her for who she is and know she could be a lot happier if she tried to get over her ED, and help her.

all you can really do is assure your girlfriend that you love her and that her happiness and wellbeing are important to you. when you're in bulimia mode it's hard to understand...sometimes you don't understand yourself why it's happening...so it's hard to explain...but you could try get your girl to let you know where she's at with it....how often she purges etc...the more she speaks( even if it is hard to hear) the more she will open up and the more in a way the power is taken from the disorder! I hope it helps even a bit...you are a great guy for hanging around...it's a difficult thing to be around!...Love and Prayers...B xx

First of all, your continued love & concern for your girlfriend is most helpful to her. I battled anorexia/bulimia for over 40 years & finally won the war. It's no different, in my opinion, than alcohol or drugs. A/B also very sad, because many times the person is too ashamed to talk about it, even (or especially) to someone they love, trying constantly to hide the facts with lies. I agree with chocowalnut that something is usually lacking in a different area of the person's life, past or present. And many times the person can't really pinpoint it. Gosh, the problem is so faceted I don't know how to make this brief or which aspects to address. But I so want to help. Wish I could talk with her. I know how she feels and how very difficult it is to stop. After a time A/B begins to feel like a monster sucking away time, health & happiness. Not to mention friends. Sometimes it takes knowing how easily it can snuff away one's life, literally, to win the battle. If you have any questions in particular you'd like to ask I'll be glad to answer. My best to you ~ ~