Heartfelt after that, almost blushing (7)
I believe the answer is:
sincere
'heartfelt' is the definition.
(similar in meaning)
'after that almost blushing' is the wordplay.
'after' becomes 'since' (since can mean after a certain time).
'that almost' means to remove the last letter (most of the word but not all of it).
'blushing' becomes 'red' (blushing makes someone's face go red).
'red' with its last letter removed is 're'.
'since'+'re'='SINCERE'
(Other definitions for sincere that I've seen before include "Open and genuine, not deceitful" , "Genuine; deceit-free" , "(Of person) genuine" , "Free from deceit" , "like informal correspondents?" .)