The most common and most likely answer to this crossword clue is the 5 plus 4 letter word DOG’S LIFE
I've seen this crossword clue in The Guardian
D
O
G
â
€
™
S
L
I
F
E
Buddy explains!
The straight part
We know that "An unhappy existence" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an unhappy existence = dog’s life.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.