I understand how hard this must be for you. I know alcohol is everywhere when you are a musician. However, when it comes right down to it, this is YOUR life. You need to stop comparing yourself to everyone else and how they can drink with no apparent side effects. You don't really know what's going on in their body. You need to know what's best for YOU. In the end, you only have yourself. If you band mates can't understand that you want to stop drinking, then they may not be the best people to be around. Simply tell them you are slowing down( or stopping) for awhile. They need no other explanation.
Best of luck to you