Boyfriend appearing outside old city office (6)
I believe the answer is:
bureau
'office' is the definition.
('bureau' can be a synonym of 'office')
'boyfriend appearing outside old city' is the wordplay.
'boyfriend' becomes 'beau' ('beau' can be a synonym of 'boyfriend').
'appearing outside' is an insertion indicator.
'old city' becomes 'ur' (ancient city state).
'beau' enclosing 'ur' is 'BUREAU'.
(Other definitions for bureau that I've seen before include "Item of furniture" , "Government department, agency" , "Piece of furniture with drawers" , "The B in the FBI" , "French office - desk" .)