He's single, to a degree (8)
I believe the answer is:
bachelor
This clue is a triple definition!
'he's' is the first definition.
(I've seen this before)
'single' is the second definition.
(I've seen this before)
'to' acts as a link.
'a degree' is the third definition.
(thesaurus)
(Other definitions for bachelor that I've seen before include "he has no ties" , "Single person" , "Single man" , "Unmarried person" , "Non-married male" .)