Hold together man's broken heart (6)
I believe the answer is:
cohere
'hold together' is the definition.
(I've seen this before)
'man's broken heart' is the wordplay.
'man' becomes 'he' (pronoun for a man).
'broken' indicates putting letters inside.
'heart' becomes 'core' (synonyms).
'he' inserted within 'core' is 'COHERE'.
(Other definitions for cohere that I've seen before include "Stick together, remain united" , "Form a whole" , "Cling" , "Even; without jerks" , "Hold firmly together" .)