Complex sentence: Their marriage lasted from April 15,1929, until his death at the age of 82 in 1979, despite Rand's affair with a much younger man Nathaniel Branden-undertaken with O'Connor's consent-who was part of her philosophical movement.
Split into simpler sentences: Their marriage lasted from April 15,1929, until his death at the age of 82 in 1979. They never divorced, despite Rand's affair with a much younger man Nathaniel Branden, who was part of her philosophical movement.