Devoted to someone, one has rewritten novel (2,4)
I believe the answer is:
in love
'devoted to someone' is the definition.
'one has rewritten novel' is the wordplay.
'one' becomes 'i' (Roman numeral).
'has rewritten' is an anagram indicator.
'novel' anagrammed gives 'nlove'.
'i'+'nlove'='IN LOVE'
(Other definitions for in love that I've seen before include "Struck by Cupid's dart" , "Consumed by romantic passion" , "Filled with romantic feeling for someone" , "Enamoured" .)