Was not happy about long note (7)
I believe the answer is:
repined
'was not happy' is the definition.
(I've seen this before)
'about long note' is the wordplay.
'about' becomes 're' (regarding).
'long' becomes 'pine' (to pine for someone is to long for them).
'note' becomes 'D' (musical note).
're'+'pine'+'d'='REPINED'
(Other definitions for repined that I've seen before include "Grudged" , "Fretted; was discontented" , "Languished" , "Regretted" , "Was not happy" .)