1
general::
Phrase(s): sweet on someone
Rur. fond of someone. (*Typically: be ~; become ~.) • Tom is sweet on Mary. He may ask her to marry him. • Mary’s sweet on him, too.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Enamored of, in love with, as in I think Barbara's sweet on Nick. This colloquial idiom was first recorded in 1740.
American Heritage Idioms