Hi Jewel,
I am a recovering alcoholic with 27 yrs of sobriety AND i am diabetic. I see lots of "red flags" and i suspect, given what you have written, that you do too. My understanding is that there are a lot of drugs and alcohol in the music industry, especially among younger musicians and groups. That statement is a general statement and certainly doesn't mean that this person is alcoholic. (It also doesn't mean he isn't, for that matter.) It also doesn't mean that he is--OR WILL EVER BECOME--diabetic. So, my first question to you would be this: what is your relationship with this man? Are you friends? A concerned fan? A lover? I ask this because part of what i would suggest you think about and/or do depends on who he is your life. I would also ask what you are most concerned about; i get the impression it is the diabetes issue but you mention the drinking in a way that makes me wonder if you are worried about that. From my standpoint, the immediate issue is the potential alcohol/substance abuse. A person who is addicted to a substance can NOT (no matter what they think!) be "present" in a relationship. So, if you are in a relationship with him and this is going on you need to think about what you want in a partnership and if this man is providing it. With substance abuse, the substance (alcohol, drugs, whatever) come FIRST! If others in the band are also heavily using it becomes more difficult to change that "culture."
Now, if you are simply a fan then i would suggest you let go emotionally and consider what is being brought up in YOU that is creating so much feeling. It seems to me that maybe it has something to do with this loss you were talking about and maybe the feeling of being so powerless to help in many situations like the one you mention. I have a sister who drank alcoholically for many years and it was hard to watch her do that and not be able to help, but i couldn't. It just doesn't work that way. If you are interested in exploring this more a good place to do that is with a program called Alanon. Also, there is a forum here (12 step recovery) where you can get more information and help. If Bret is a personal friend you can also get help learning how to talk to him about your fears.
The bottom line from my perspective is this: you need to take care of YOU so that YOU are healthy (emotionally, spiritually and physically) and, in that way, ensure that people in your life who are important to you are also healthy, giving you the best chance of having a wonderful, happy and fulfilling life.
Good luck to you, Jewel.
pat d