Before I have left at the end, he’s certain to cry (6)
I believe the answer is:
snivel
'cry' is the definition.
(sniveling is a kind of crying)
'before i have left at the end he's certain' is the wordplay.
'before' is a charade indicator (letters next to each other).
'i have' becomes 'I've' (contraction of 'I have').
'left' becomes 'l' (common abbreviation).
'at the end' suggests the final letters.
The last letters of 'hes certain' are 'sn'.
'ive'+'l'='ivel'
'ivel' put after 'sn' is 'SNIVEL'.
'to' acts as a link.
(Other definitions for snivel that I've seen before include "Blub revoltingly" , "Complain self-pityingly" , "moan" , "Blubber contemptibly" , "Complain tearfully" .)