how is "love" defined in the story?

Dantès declares himself an exile from humanity during the years in which he carries out his elaborate scheme of revenge. He feels cut off not only from all countries, societies, and individuals but also from normal human emotions. Dantès is unable to experience joy, sorrow, or excitement; in fact, the only emotions he is capable of feeling are vengeful hatred and occasional gratitude. It is plausible that Dantès’s extreme social isolation and narrow range of feeling are simply the result of his obsession with his role as the agent of Providence. It is not difficult to imagine that a decade-long devotion to a project like Dantès’s might take a dramatic toll on one’s psychology.

Yet Dantès’s alienation from humanity is not solely due to his obsessive lust for revenge but also to his lack of love for any living person. Though he learns of his enemies’ treachery years before he escapes from prison, his alienation from humanity begins to take hold only when Abbé Faria dies. Until Faria’s death, Dantès’s love for Faria keeps him connected to his own humanity, by keeping the humanizing emotion of love alive within him. When Dantès learns that his father is dead and that Mercédès has married another man, his alienation is complete. There are no longer any living people whom he loves, and he loses hold of any humanizing force.