Observe they've caught discontented partner involved in romp (5)
I believe the answer is:
spree
'romp' is the definition.
(I've seen this in another clue)
'observe they've caught' is the wordplay.
'observe' becomes 'see' (observe can mean to see something).
'they've' becomes 'pr' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'caught' is an insertion indicator.
'see' going around 'pr' is 'SPREE'.
'discontented partner involved in' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for spree that I've seen before include "Drinking bout" , "booze-up?" , "night on the razzle?" , "Session of over-indulgence" , "Unrestrained time" .)