The most common and most likely answer to this crossword clue is the 9 letter word BIPARTITE
I've seen this crossword clue in The Guardian
B
I
P
A
R
T
I
T
E
Buddy explains!
The straight part
We know that "Bet pair’s involved with it, if so" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bet pair’s involved with it, if so = bipartite.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 BIPARTITE mean?
BIPARTITE adjective- Having two parts.
- (of an agreement or contract) Having two participants; joint.
- (of leaves) Divided into two at the base.
- (of a graph) Having vertices that can be divided into two independent sets (see bigraph)