Pure ecstasy filling boy next to girl (9)
I believe the answer is:
unalloyed
'pure' is the definition.
(similar in meaning)
'ecstasy filling boy next to girl' is the wordplay.
I cannot quite understand how this works, but
'ecstasy' could be 'e' (informal term for the drug) and 'e' is found in the answer.
'boy' could be 'lloyd' and 'lloyd' is found within the leftover letters.
'girl' could be 'una' (girl's name) and 'una' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for unalloyed that I've seen before include "Pure, not a blend or mixture" , "Not mixed with another metal" .)