Perhaps bitter about performing solo (5)
I believe the answer is:
alone
'solo' is the definition.
(I've seen this before)
'perhaps bitter about performing' is the wordplay.
'perhaps bitter' becomes 'ale' (type of beer).
'about' is an insertion indicator.
'performing' becomes 'on' (as in being on stage).
'ale' placed around 'on' is 'ALONE'.
(Other definitions for alone that I've seen before include "Isolated from others" , "Unaccompanied" , "Exclusively, by oneself" , "unique" , "Solo" .)