The repetition, with its "sinister tone," emphasizes Nostromo's embrace
of Teresa's viewpoint, that it is up to him alone to get rich in the world. The
"previous conversation" has a sly second reference to Nostromo and Monygham's
conversation back in Chapter 2-7, when Monygham declared that Nostromo should
take the whole treasure for himself.
The "desperate affair" refers on the surface to his mission with the
silver (which is what Nostromo called it at the time )
but given his new perspective it now clearly refers to the "desperate affair"
of making his own way in the world without being exploited by the rulers, as Teresa
said, and perhaps the "desperate affair" of taking the whole treasure
for himself, as Monygham said.