Finally goes below to split them up (6)
I believe the answer is:
sunder
'split them up' is the definition.
I can't judge whether this definition defines the answer.
'finally goes below' is the wordplay.
'finally' suggests the final letters.
'below' becomes 'under' (synonyms).
The last letter of 'goes' is 's'.
's'+'under'='SUNDER'
'to' is the link.
Can you help me to learn more?
(Other definitions for sunder that I've seen before include "Cut" , "Separate the odd red sun" , "Red sun could part" , "Tear apart, sever" , "Break or tear apart, maybe a relationship" .)