Because Jeremy’s heart is honest and true (7)
I believe the answer is:
sincere
'honest and true' is the definition.
(sincere means genuine)
'because jeremy's heart' is the wordplay.
'because' becomes 'since' (I've seen this in another clue).
'heart' indicates the central letters.
The middle letters of 'jeremy' are 're'.
'since'+'re'='SINCERE'
'is' is the link.
(Other definitions for sincere that I've seen before include "devout" , "Perfect" , "(Of person) genuine" , "Not hypocritical" , "Free from deceit" .)