Malachy McCourt, who died last Monday aged 92, said the smartest thing he ever did in his life was to marry Diana Galin after they had an on-off tempestuous affair.  Few would have expected to hear him speak so candidly about his devotion to his wife. They married 59 years ago and their sanctuary was the apartment they shared on the fashionable Upper West Side of Manhattan for the rest of their lives.  Publicly acknowledging his gratitude to Diana after their 60-something years together came after he became a terminally ill patient in a New York hospice last year. His…