Couple ultimately bound to run away together (5)
I believe the answer is:
elope
'run away together' is the definition.
(I've seen this before)
'couple ultimately bound' is the wordplay.
'ultimately' suggests the final letters.
'bound' becomes 'lope' (to lope is to travel with bounding stride or bound).
The last letter of 'couple' is 'e'.
'e'+'lope'='ELOPE'
'to' is the link.
(Other definitions for elope that I've seen before include "Bolt" , "Run away together" , "Do a runner" , "Abscond for amorous purposes" , "leave with lover" .)