Bulimia Question, Please Help, Very Important!!?

Okay, so I have a friend (Friend A) who got in a fight with another friend (Friend B). I pried quite a bit, and finally Friend A told me that Friend B was mad at Friend A, because Friend A found out that Friend B was bulimic. Now obviously Friend A is scared for Friend B, and wants to help, but Friend A thinks that if Friend B were to ever forgive them, they'd have to never tell about Friend B's bulimia problem. Now, Friend A knew that I wouldn't tell Friend B that I knew about Friend B's problem, so they told me. Friend A doesn't have the balls to get help for Friend B, so what do I do? Friend A will probably be mad at me if I try to get Friend B help, but ? What do I do? Who would I tell? What would I say, because telling anyone that a friend of a friend has bulimia is not very believable. I want to help Friend B without Friend A getting mad at me, but how would I do that? Someone answer, because I have to help this poor kid.!!