Chances are if you felt uncomfortable then others felt it too. Hopefully he doesnt come again. Support groups are supposed to be supportive and safe. Can you get there early the next time you go and speak with the facilitators and voice your concerns to them? It would be a pity not to say something when you are enjoying the group. If all else fails leave during the group and say you are unwell. Nobody has to know specifics. I wish you well in seeing this through.