Unfaithful type at his wit's end taking pill (7)
I believe the answer is:
atheist
'unfaithful type' is the definition.
(I've seen this before)
'at his wit's end taking pill' is the wordplay.
'end' suggests the final letters.
'taking' indicates putting letters inside.
'pill' becomes 'e' (ecstasy).
The last letter of 'wit' is 't'.
'his'+'t'='hist'
'hist' going around 'e' is 'heist'.
'at'+'heist'='ATHEIST'
(Other definitions for atheist that I've seen before include "Person who does not believe in existence of a god" , "Disbeliever in deities" , "I don't believe" , "One disbelieving in the existence of God or gods" , "One who believes there is no god" .)