Playful behaviour brings end of old association (9)
I believe the answer is:
Here is my best explanation:
'playful behaviour' is the definition.
'end of old association' is the wordplay.
'end of old' becomes 'd' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'association' becomes 'alliance' (I've seen this before).
'brings' is the link.
(Other definitions for dalliance that I've seen before include "Toying - trifling - delay", "Flirtation", "affair", "Fling", "Playing", "Trifling", "Affair", "Delay", "Casual relationship" and "time-wasting action".)