it's true, you can't get involved. try to get a real life for yourself - separate from him - rather than living his. if you want to help him with the bulimia, carefully drop a hint to people who care about him, friends, parents, teachers, but better not his new gf.
even if it's very hard, try not to contact him for at least a year, and you'll be able to be great friends later on. good luck.

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