Small youngster got illuminated and separated (5,2)
I believe the answer is:
split up
'separated' is the definition.
(split up can mean separated or divorced)
'small youngster got illuminated' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'youngster' becomes 'pup' (a pup is a young dog).
'got' means one lot of letters goes inside another.
'illuminated' becomes 'lit' (synonyms).
'pup' enclosing 'lit' is 'plitup'.
's'+'plitup'='SPLIT UP'
'and' is the link.
(Other definitions for split up that I've seen before include "Separate" , "End a relationship" , "Part company" , "Parted company" , "Divorce" .)