Girl's placed before sweetheart, causing argument (7)
I believe the answer is:
dispute
'argument' is the definition.
(thesaurus)
'girl's placed before sweetheart' is the wordplay.
'girl's' becomes 'dis'.
'placed' becomes 'put' (I've seen this in other clues).
'before' means one lot of letters go next to another.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'dis'+'put'+'e'='DISPUTE'
'causing' is the link.
(Other definitions for dispute that I've seen before include "Argue about (something)" , "Question or deny accuracy or validity" , "conflict" , "Argument, contention" , "Disagree or challenge" .)