Why does Fortunato continue underground among the catacombs when the nitre is making him cough?

He wants to taste the amontillado (type of red wine) and he doesn't want Luchesi to taste it. Luchesi is Fortunato's competitor.

HOPE THIS HELPS :)

This story is really confusing and difficult to understand, I had to read it over 3 times to understand the whole story.