I don't believe you become celibate? (4,3,2)
I believe the answer is:
come off it
'i don't believe you' is the definition.
('come off it' is an expression of disbelief)
'become celibate?' is the wordplay.
I cannot really see how this works, but
'become' could be 'come' (synonyms) and 'come' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for come off it that I've seen before include "Don't make me laugh" , "stop behaving like that!" , "Don't talk rubbish" , "You're mad!" , "get down from there" .)