What can i do to help bipolar/bulimic friend who cuts?

Encourage treatment: Cutting, bulimia, and bipolar disorder are serious and persisting conditions that require professional help. While it is admirable and kind of you to help a friend, unless you are also professionally trained, you are unlikely to successfully help them manage their illness. Be kind, but persistent in your stance that they receive professional help. Offer to go with them if it helps.