Being by herself Nelly is confused about love (6)
I believe the answer is:
'being by herself' is the definition.
I can't tell whether this definition defines the answer.
'nelly is confused about love' is the wordplay.
'is confused' indicates an anagram.
'about' indicates putting letters inside.
'love' becomes 'o' (love means zero in tennis).
'nelly' with letters rearranged gives 'lnely'.
'lnely' placed around 'o' is 'LONELY'.
Can you help me to learn more?
(Other definitions for lonely that I've seen before include "Without companionship" , "Unhappily unattached persons?" , "without friends" , "Solitary and sad" , "Missing company" .)