Of course Fortunado, you're not going to die of a cough
Do you want to turn back? Your cough is getting worse.
No, we must get the Amontillado no cough is going to kill me.
Fortunado was making fun of Montressor and his family which angered Montressor into wanting to kill Fortunado with impunity
At the Carnival Theme, Montressor was trying find Fortundao, he did and already is drunk, half of his plan is done. Montressor is telling Fortunado that he has The Amontillado and he's needs someone to identify it Fortunado agrees to come.
In the catacombs to retrieve the Amontillado, Montressor ask Fortunado multiple times if he wants to turn back because if his illness, but because he's not going to die to a mere cough so they proceeded
Fortunado just realized that he was chained against the wall while Montressor was looking and gazing at him as it was him that chained him.
While Fortunado was yelling and screaming at Montressor, he was building a wall block the small room with Fortunado inside.
Montressor build the wall while Fortunado was crying in agony of wanting to be free, Montressor played with him until he could hear no more. Montressor walked away and got his revenge.