Foolishly agree with Lot's confidant (5,3)
I believe the answer is:
alter ego
'confidant' is the definition.
('alter ego' can be a synonym of 'confidant')
'foolishly agree with lot's' is the wordplay.
'foolishly' indicates anagramming the letters.
'with' says to put letters next to each other.
'agree'+'lot'='agreelot'
'agreelot' with letters rearranged gives 'ALTER EGO'.
(Other definitions for alter ego that I've seen before include "'One's alternative personality (5,3)'" , "Similar character" , "Is it Kent" , "One's secondary personality" , "Other self - large toe (anag)" .)