Unemotional sex rejected in novel (8)
I believe the answer is:
reticent
'unemotional' is the definition.
(I know that unemotional can be written as reticent)
'sex rejected in novel' is the wordplay.
'sex' becomes 'it' (common euphemism).
'rejected' shows that the letters should be reversed in order.
'in' indicates putting letters inside.
'novel' becomes 'recent' (both can mean new).
'it' in reverse letter order is 'ti'.
'ti' placed into 'recent' is 'RETICENT'.
(Other definitions for reticent that I've seen before include "'Self-effacing, restrained (8)'" , "Secretive" , "Not forthcoming" , "Disinclined to speak" , "Uncommunicative" .)