You are briefly trapped in boyfriend's desk (6)
I believe the answer is:
bureau
'desk' is the definition.
(type of writing desk)
'you are briefly trapped in boyfriend's' is the wordplay.
'you are briefly' becomes 'ur' (text or internet abbreviation; 'briefly' suggests an abbreviation).
'trapped in' indicates putting letters inside.
'boyfriend' becomes 'beau' (synonyms).
'ur' placed within 'beau' is 'BUREAU'.
(Other definitions for bureau that I've seen before include "Office; writing desk" , "Agency - writing desk" , "Piece of furniture with drawers" , "Room" , "Writing desk with drawers" .)