Leave day set apart to have a relationship (2,6)
I believe the answer is:
go steady
'apart to have a relationship' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'leave day set' is the wordplay.
I cannot quite see how this works, but
'leave' could be 'go' (to go is to depart or leave) and 'go' is found within the answer.
an anagram of 'day' is 'ady' which is located in the answer.
an anagram of 'set' is 'ste' which is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for go steady that I've seen before include "Keep seeing each other" , "Have relationship as regular boy or girl friend - sounds stable" , "Court romantically" , "See someone regularly" , "Date one person regularly" .)