In the plot of the opera Madame Butterfly, what is the relationship between Pinkerton and Sharpless? How does that story relate to Gallimard?

Sharpless is an American diplomat. He serves as Pinkerton's voice of reason in the story. Even though Gallimard casts himself as Pinkerton, this is not the case of Gallimard's real life, since Marc was always the lecherous one while Gallimard was always the more collected personality.