In "The Cask of Amontillado," is it possible that Montressor is jealous and Fortunato never did as many things as he says? Montressor mentions,...

The line you refer to is suggestive of sarcastic jealousy but I think the real motivation for Montresor's crime is a little deeper. If you read the first line of the story, Montresor says he had borne a thousand injuries but it was when Fortunato insulted him that he vowed revenge. Later in the story, Fortunato says,"Oh I forgot, the Montresors were once a rich and noble family". That statement, together Montresor's coat of arms and a family motto that says "No on insults me with impunity" is Poe's clue to the reader that Fortunato insulted Montresor's family in some way. Fortunato is also too proud. He is proud of his wine tasting ability, proud of his membership in the masons, and he's drunk far too much wine. That's why Montresor keeps giving him so much wine, to take away any judgment or mistrust Fortunato might normally had had. Granted, Montresor was jealous of Fortunato, because Fortunato was still rich and respected. But, the last straw was Fortuanato's insult, probably committed unknowingly, that prompted Montresor's revenge.