Thought shortlist would be given to sweetheart whom they regard as perfect (8)
I believe the answer is:
idealise
'regard as perfect' is the definition.
(I've seen this before)
'thought shortlist would be given to sweetheart whom they' is the wordplay.
I cannot really understand how this works, but
'thought' could be 'ideal' (ideal is a kind of thought) and 'ideal' is located in the answer.
'sweetheart' could be 'e' (the heart/centre of 'sweet') and 'e' is found within the answer.
The remaining letters 'is' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for idealise that I've seen before include "Consider something or someone perfect" , "Treat as perfect (S, not Z)" , "Think of as perfect" , "Regard as perfect" , "Have unrealistic picture of" .)