No. The Godfather novel is mainly about the Corleone crime family's power struggles, loyalty, and family dynamics, not about sexual scenes involving Sonny in that way.
The main themes are power and its acquisition and maintenance. The Corleone family is constantly vying for more power in the criminal underworld. Another theme is family loyalty. Despite all the illegal activities, family members stand by each other.
They might be characters from a specific genre of story. For instance, if it's a romantic comedy, Sonny could be a bubbly girl and Chad a bit of a shy but charming guy. They could be neighbors or coworkers, and their relationship develops in a humorous and heartwarming way.
Sonny might become more confident in her relationships. The kiss could make her realize that she can be bold in matters of the heart. Chad, on the other hand, might become more vulnerable. He has always been a bit of a ladies' man, but this kiss could change his approach to relationships.
Sonny might be a werewolf pup who has a problem with Mommy, who could be Leah as a mother - like figure in the werewolf pack. The 'shut up' comment could stem from Sonny's disagreement with Mommy's decisions regarding pack matters, like how to deal with the vampires in their territory.
Other than 'The Godfather', there were also some similar gangster novels that could be recommended. Among them,"The Corleone Family" was a derivative work of "The Godfather." With Santino as the main character, it told the story of the Corleone Family's rise in the 1930s. This novel continued the narrative technique and dialogue form of The Godfather. The character creation and storyline were excellent, and it was considered the best derivative novel of The Godfather. In addition,"The Door of the Sheep"(also known as "The Heavenly Person") was an officialdom novel. Although it was not an underworld novel, it was similar to "The Godfather" in interrogating people's hearts and humanity. It was recommended to readers who liked "The Godfather."
One plot idea could be that after the kiss, they struggle to define their relationship in the context of their showbiz world. They might face pressure from the studio or fans.