I'm sorry to hear about your brother. It does sound like he has a problem, however worrying will only do you harm and won't help him. He has to realize he has a problem and want help. I would suggest that you use the Serenity Prayer to help you deal with the issue.
God grant me the serenity
to accept the things I cannot change;
courage to change the things I can;
and wisdom to know the difference.

I have found this to be very helpful in reminding myself of the things I can do and that I can't do. My dad was an alcoholic, so I know it is not easy to watch someone go down this path.