YOU SAID:

i have fallen hard for him

INTO JAPANESE

私は彼にすっかり恋に落ちてしまいました

BACK INTO ENGLISH

I fell madly in love with him

INTO JAPANESE

私は彼に夢中になって恋に落ちました

BACK INTO ENGLISH

i fell in love with him

INTO JAPANESE

私は彼に恋をした

BACK INTO ENGLISH

i fell in love with him