Emperor in love with America becomes demanding (7)
I believe the answer is:
onerous
'demanding' is the definition.
(thesaurus)
'emperor in love with america' is the wordplay.
'emperor' becomes 'nero' (Roman emperor).
'in' is an insertion indicator.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'with' is a charade indicator (letters next to each other).
'america' becomes 'us' (abbreviation for the United States**).
'o'+'us'='ous'
'nero' placed into 'ous' is 'ONEROUS'.
'becomes' acts as a link.
(Other definitions for onerous that I've seen before include "Burdensome as duty may be" , "Burdensome, taxing" , "Burdensome, demanding" , "Involving much effort" , "No euros? That's burdensome" .)