fall in love
idiom.idiom. to start having romantic feelings for someone.
idiom. An intransitive verbal idiom meaning to begin to experience romantic feelings for someone, typically followed by 'with' to introduce the object of affection.
They fall in love in the movie.
He didn't expect to fall in love with his best friend, but it happened.
Despite their families' long-standing feud, the two protagonists inevitably fall in love, setting the stage for the play's tragic conclusion.
The person you love is introduced with the preposition 'with'.
Contrast 'fall in love' (the process of starting to love someone) with 'be in love' (the state of loving someone).
He fell in love to her.He fell in love with her.The preposition 'with' is required to connect the phrase to the person you love.