Only Fools Fall in Love

Daai lo baai sau is a movie starring Roy Chiao, Shing-Chi Fung, and Vincent Kok. The story of a rich man who looses his memory and a girl who cares for him trying to get him back to normal.
Poor girl meets rich boy as they quarrel over a food seller's once a year delicacy. His brother pays her to marry the brother so he can stage an assassination attempt. The attempt doesn't succeed but the man is reduced to the level of an idiot child and the girl looks after him because of her guilt. She nurses him back to health so that he can resume his place as head of the family.