It ends happily and with relief (5)
I believe the answer is:
siege
This clue could be a double definition.
'it ends happily and' is the first definition.
The definition suggests a singular noun which matches the answer.
'relief' is the second definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'with' is the link.
Can you help me to learn more?
(Other definitions for siege that I've seen before include "Offensive encirclement" , "Action that isolates and attacks" , "Besetting" , "Persistent attempt to gain" , "Isolating attack" .)