Final answer:
Little Otis Ormonde is the character who unintentionally reveals suspicions about Bob and Gwen cheating at poker night during a bridge party.
Step-by-step explanation:
The character who inadvertently spills the beans about the suspicion of Bob and Gwen cheating at poker night is Little Otis Ormonde. The situation arises during a bridge party within the storyline, where Bernice experiences rising uneasiness due to accidentally offending Marjorie. As the conversation opens up, Little Otis Ormonde precipitates the storm, indicating that he is the one who makes the revelation about the alleged cheating, although this particular narrative detail is not present in the provided excerpts.