Lonely end to the working week, going on for ever (10)
I believe the answer is:
friendless
'lonely' is the definition.
(not having any friends)
'end to the working week going on for ever' is the wordplay.
'end to the working week' becomes 'Fri' (Friday).
'going on for ever' becomes 'endless' (I can't justify this - if you can you should give a lot more credence to this answer).
'fri'+'endless'='FRIENDLESS'
Can you help me to learn more?
(Other definitions for friendless that I've seen before include "such as Billy-No- Mates" , "Unpopular" , "solitary" , "lonely" , "lacking possibilities for socialising?" .)