The most common and most likely answer to this crossword clue is the 4 plus 2 plus 6 letter word GOES TO PIECES
I've seen this crossword clue in The Guardian
G
O
E
S
T
O
P
I
E
C
E
S
Buddy explains!
The straight part
We know that "is falling apart" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case is falling apart = goes to pieces.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.