I'd stop attending meetings, does he need to keep up membership for insurance purposes? If not, stop paying the dues.
If you are from a small town, being as non-confrontational as possible is probably the best way to go. The risk of scandal with a big to-do about leaving is serious, but leaving quietly in a dignified manner is more likely to bring about trust and respect, which help others in the direction of the truth more than a blowout.
I'm sure many of us have scandalized others by our new found zeal, and put them off in such a way that may prevent "conversion". Speaking from experience, here.