No heart gets broken by someone else (7)
I believe the answer is:
another
'someone else' is the definition.
(I've seen this before)
'no heart gets broken' is the wordplay.
'gets broken' is an anagram indicator.
'no'+'heart'='noheart'
'noheart' is an anagram of 'ANOTHER'.
'by' is the link.
(Other definitions for another that I've seen before include "Someone else" , "A different one" , "Player or person not yet named or selected" , "A different (thing)" , "A further (item)" .)