Answer:
At the end...
Montressor one day decided that he wanted to become friends with Fortunato.
Fortunato insulted Montressor about not doing good in school and life.
Montressor stopped being friends with Fortunato because all the insults he received.
Fortunato still considered Montressor a friend, but not an important one, even though he would always insult him.
Montressor was truly angry with this, that he lured Fortunato into a catacomb where he keeps his wine under his house and left him to die.
Step-by-step explanation: