According to the Daily Mail, Al Pacino's biggest regret is never marrying Diane Keaton.
I know he will forever regret he didn’t make his move when he had the chance
Pacino and Keaton played a married couple in Francis Ford Coppola’s Godfather trilogy and had an on-and-off affair from 1971 to 1987.
A friend of Pacino’s said:
Looking back, Al admits the love of his life was Diane who he’s always called, ‘an amazing woman’
Author's summary: Al Pacino regrets not marrying Diane Keaton.