Answer and Explanation:
Montressor and Fortunato begin the plot by appearing to have been good friends. This friendship is shown by the insane thoughts of Montressor, who is already planning his revenge and shows signs of madness and mental disturbance.
This narration by Montressor shows us that this friendship did not last long and that this is what will lead us to the great moment of history, the moment when revenge takes place.
That's because, something happened between Montressor and Fortunato, which triggered the disturbance of Montressor, however, while planning and preparing his revenge, he maintained his friendship with Fortunato, pretending intimacy and complicity between them, making Fortunato feel safe in the presence of friend and with that, allowing the story to develop.
The end of interactions between the two friends promotes the end of the story. This happens when Montressor, in an act of insanity, pinns his friend to the wall and leaves him there, slowly languishing to death.