Bulimia

I have a really good friend who would throw up to lose weight in middle school. I didn't find out until later on even though I saw how fast she lost weight. She was a heavier girl but now is thin for her height. Fast forward to college and she called to tell me she's been thinking about it again. What can I do or say?? I feel helpless. She doesn't want me to mention it to her boyfriend, which I respect, but I know he might have to find out eventually...(he knows about her past). I know this is a personal issue but does anyone have any advice?