Guy has date with his mistress.
On the way to the date he sees somebody who looks like his best friend, follows him, and when he discovers that it's not his best friend challenges him to a duel for the insolence of looking like his best friend.
Therefore, he is late to his date, explains to his mistress why and also gushes a lot about his best friend. When mistress gets annoyed about this he explains 'Well I love you more than any woman but I love him more than any human'