if all it takes is an alcoholic seeing someone else take a drink to fall off the wagon, then maybe he shouldnt be in public places where the consumption of alcohol is going to occur like restaurants or sporting events. if he is that weak he should not to put himself in such precarious situations.
But see, he was going to you for spiritual strength to resist in drinking. Besides, lets say you were at your church or somebody else's house where he did not know alcoholic beverages would be present. What then?