Pair watches partners being unfaithful (3-6)
I believe the answer is:
Here is my best explanation:
I believe this clue is a double definition.
'pair watches' is the first definition.
(a pair of watches is two timers)
'partners being unfaithful' is the second definition.
(two-timing is cheating)
(Another definition for two-timers that I've seen is "Traitors".)