Break off with Ambrose, very obsessive (5)
I believe the answer is:
sever
'break off' is the definition.
(I've seen this before)
'with ambrose very obsessive' is the wordplay.
'with' says the answer is hidden in the clue.
'SEVER' is hidden in the letters of 'ambrose very obsessive'.
(Other definitions for sever that I've seen before include "Cut off suddenly" , "Cut from a whole" , "Cut or break off, perhaps a relationship" , "Cut apart, maybe a relationship" , "Verse (anag)" .)