I understand your fear. You have a huge decision to make. You can drink with them and bring back all the hell that goes with it or you can stay sober and remain on the road to recovery. Do you really think you can play the designatied driver role and not drink in this situation? That doesn't sound like a wise move to me. I'm thinking you need to stand firm, tell your brother whats going on with you and how important it is for you to stay sober and stay away from people, including your brother, when they are getting drunk. Also, it may be time for you to get involved with AA. I wish you all the best.