Cause of suffering — not having a second bottle! (7)
I believe the answer is:
scourge
'cause of suffering' is the definition.
(I've seen this before)
'not having a second bottle' is the wordplay.
'not having' is a deletion indicator.
'second' becomes 's' (common abbreviation).
'bottle' becomes 'courage' (I've seen this before).
's'+'courage'='scourage'
'scourage' with 'a' removed is 'SCOURGE'.
(Other definitions for scourge that I've seen before include "form of punishment" , "Person/thing causing great suffering; whip" , "source of evil" , "Whip; agent of suffering" , "Curse; whip" .)