Questions & Answers about Er verliebt sich in sie.
Why does this sentence use in when the English translation says "with"?
In German, prepositions rarely translate one-to-one. The verb sich verlieben (to fall in love) always pairs with the preposition in. You can think of it as falling into love with someone. You cannot use mit (with) here.
How would I ask "Who is he falling in love with?" based on this sentence?
Because the verb uses the preposition in and refers to a person, you form the question by combining in with the accusative question word wen (whom/who). So, you would ask: In wen verliebt er sich?
Is sie in the accusative or dative case in this sentence?
It is in the accusative case. The preposition in always takes the accusative case when it is used with the verb sich verlieben. Even though sie (she/her) looks the same in both the nominative and accusative forms, it is acting as the accusative object here.
What is the sich doing in this sentence?
The German verb for "to fall in love" is reflexive: sich verlieben. You have to use a reflexive pronoun with it, similar to saying "he infatuates himself" in English. Because the subject is er (he), the matching reflexive pronoun is sich.