Cleave to - had come adrift before (6)
I believe the answer is:
adhere
'cleave' is the definition.
(I've seen this in another clue)
'had come adrift before' is the wordplay.
'come adrift' is an anagram indicator (I've seen 'comes adrift' mean this (I've seen this in other clues)).
'before' becomes 'ere' (poetic term for 'before').
'had' anagrammed gives 'adh'.
'adh'+'ere'='ADHERE'
'to' acts as a link.
(Other definitions for adhere that I've seen before include "Stick like a stamp" , "Bond" , "Stick to, remain loyal" , "Stick fast (to something)" , "Stick to or remain faithful" .)