The most common and most likely answer to this crossword clue is the 9 letter word OBSESSING
I've seen this crossword clue in Financial Times
O
B
S
E
S
S
I
N
G
Buddy explains!
The straight part
We know that "Haunting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case haunting = obsessing.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.
What does OBSESSING mean?
OBSESSING verb- (passive, constructed with "with") To be preoccupied with a single topic or emotion.
- To dominate the thoughts of someone.
- (construed with over) To think or talk obsessively about.