Paid back though completely in the red (8)
I believe the answer is:
requited
'paid back' is the definition.
(I've seen this before)
'completely in the red' is the wordplay.
'completely' becomes 'quite' (synonyms in phrases like 'are you quite done?').
'in' indicates putting letters inside.
'quite' put into 'red' is 'REQUITED'.
'though' is the link.
(Other definitions for requited that I've seen before include "Repaid appropriately" , "Paid back" , "Returned as love may be" .)