Move gradually away — ultimately sad breach (5)
I believe the answer is:
drift
'move gradually away' is the definition.
'ultimately sad breach' is the wordplay.
'ultimately' suggests the final letters.
'breach' becomes 'rift' (I've seen this before).
The final letter of 'sad' is 'd'.
'd'+'rift'='DRIFT'
(Other definitions for drift that I've seen before include "Walk casually; snow pile" , "state of indecision" , "Tendency" , "Move casually or aimlessly" , "move around without end" .)