fall in love with sb
idiom.idiom. To start having strong romantic feelings for someone.
idiom. An idiomatic verbal phrase describing the onset of romantic feelings for a person, followed by the preposition 'with' to introduce the object of affection.
He might fall in love with her.
They met on holiday and quickly fell in love with each other.
Despite their families' long-standing feud, the two protagonists inevitably fall in love with one another, setting the stage for the play's tragic conclusion.
The object of affection is introduced by the preposition 'with'.
Contrast with 'have a crush on' (less serious, often one-sided) and 'be in love with' (describes the state, not the beginning of it).
He fell in love on her.He fell in love with her.The correct preposition to connect the feeling to the person is 'with'.