Never returning. Endlessly using second levels (5)
I believe the answer is:
evens
'levels' is the definition.
('even' can be a synonym of 'level')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for evens that I've seen before include "Balanced odds" , "straight bet" , "decreases" , "These are odds, strangely" , "Level betting" .)