Pretend friend gets you locked up in reality (8)
I believe the answer is:
actually
'in reality' is the definition.
(synonyms)
'pretend friend gets you locked up' is the wordplay.
'pretend' becomes 'act' (I've seen this in other clues).
'friend' becomes 'ally' (an ally is a friend or supporter).
'gets' is a charade indicator (letters next to each other).
'you' becomes 'u' (commonly used in online communication).
'locked up' indicates putting letters inside.
'act'+'ally'='actally'
'actally' going around 'u' is 'ACTUALLY'.
(Other definitions for actually that I've seen before include "Really existing" , "In reality" , "As a matter of fact" , "A lay cult may be existing in fact" , "Really, in fact" .)