I help with errand, working for Casanova (11)
I believe the answer is:
philanderer
'casanova' is the definition.
(thesaurus)
'i help with errand working' is the wordplay.
'with' says to put letters next to each other.
'working' indicates anagramming the letters.
'i'+'help'+'errand'='ihelperrand'
'ihelperrand' with letters rearranged gives 'PHILANDERER'.
'for' is the link.
(Other definitions for philanderer that I've seen before include "Casual lover" , "Male flirt" , "Womaniser, libertine" , "wolf" .)