I'm looking for an old story about a brother and a sister.
One of the scenes is that the brother invites a friend to come have sex with the sister and after the friend has sex with her, the brother then hasn't sex with her too in front of the friend.
And another scene is the end of the story where the sister is babysitting and invites the brother over. The sister has sex with the boy she's babysitting while the brother is playing with his ass. And then the brother ends up having anal sex with the boy. I think the final scene is the sister has sex again with the boy and let's him cum in her. Showing the brother that she loves the boy.