Nie Huaisang asks Jiang Cheng to plug him up after sex so he can be filled with Jiang Cheng's cum while presiding over a discussion conference. Halfway through the day, Jiang Cheng thinks he should check if Huaisang needs a refill.
"The half-eaten peach" was a reference to homosexuality in ancient China (just like "cut sleeve"), you can read about why here.
This is Nie Huaisang's bedroom, just fyi:
Imported from Archive of Our Own. Original work id: 38312149.