The verb ‘fantasize’ is typically followed by the preposition ‘about’ when referring to someone imagining a pleasant situation that is unlikely to happen.

১. Fantasize ‘with’ or ‘from’ is grammatically incorrect in the context of imagining future possibilities.
২. ‘Fantasize about’ indicates the subject or content of the daydream or imagination.
৩. Using ‘after’ would change the meaning to something occurring after the event, which doesn’t fit the dream-like context.

অতিরিক্ত তথ্য: Certain verbs in English have fixed prepositions, known as appropriate prepositions.