Need to be without others, showing malice (8)
I believe the answer is:
wantonly
'showing malice' is the definition.
'need to be without others' is the wordplay.
'need' becomes 'want' (want is a kind of need).
'to be without others' becomes 'only'.
'want'+'only'='WANTONLY'
(Other definitions for wantonly that I've seen before include "Arbitrarily" , "in an immoral way" , "in an extravagant way" , "In a reckless unrestrained way" , "In irresponsible way, lacking proper restraint" .)