This is a classic al-anon situation and I'd highly recommend that group for anyone who has someone in their life struggling with any type of addiction. It helps you deal with what's your problem and what's not your problem. I try to be supportive by giving praise when the person/addict is doing things well, and when they are struggling ask only genuine, open-ended questions like, 'how's it going with you latest diet?" And I ask those sparingly.