Montresor kills Fortunato, so he gets the revenge he feels he deserves and rids himself of a perceived adversary, but there is no real sense that he resolves his conflict with his enemy. To resolve a conflict would involve, at the least, talking it out, and this never happens.
Although Montresor asserts that Fortunato has injured him a thousand times, during the course of the story, Fortunato appears completely unaware that Montresor has any reason to be angry with him. Montresor himself says he has hidden his anger well, smiling and being friendly to Fortunato so that he can more easily get vengeance.
While he sobers up and recognizes he is being walled up in a catacomb, Fortunato undoubtedly realizes that Montresor is upset with him for some reason, but he seems to have no idea what the problem is. Fortunato has no opportunity to apologize or, conversely, to explain how what happened was a misunderstanding. Montresor simply leaves him to perish.