The most common and most likely answer to this crossword clue is the 3 plus 5 plus 5 letter word ONE NIGHT STAND
I've seen this crossword clue in The Guardian
O
N
E
N
I
G
H
T
S
T
A
N
D
Buddy explains!
The straight part
We know that "Joined item in bedroom/it won’t happen again!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case joined item in bedroom/it won’t happen again! = one night stand.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.