In ticking off his credentials on the campaign trail — management consultant, businessman, governor — Mitt Romney omits what may have been his most distinctive post: Mormon lay leader, offering pastoral guidance on all manner of human affairs from marriage to divorce, abortion, adoption, addiction, unemployment and even business disputes. Bryce Clark was a recipient of Mr. Romney’s spiritual advice. Late one summer night in 1993, distraught over his descent into alcoholism and drug use, Mr. Clark, then a 19-year-old college student, decided to confess that he had strayed from his Mormon faith. So he drove through this well-heeled Boston suburb to Mr. Romney’s secluded seven-bedroom home.