The most common and most likely answer to this crossword clue is the 10 letter word COEXISTENT
I've seen this crossword clue in Independent
C
O
E
X
I
S
T
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N
T
Buddy explains!
The straight part
We know that "Living together" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case living together = coexistent.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 COEXISTENT mean?
COEXISTENT noun- That which coexists with another.
- Existing at the same time as something else