And the nerd turned out to be quite good! I thought he was so thoroughly licking her asshole. Turns out he's an anal gourmet. He's been shoving it all the way up her asshole. Apparently this wasn't the first time the lovers had tried it - the bitch didn't even twitch when he came in. She's got an asshole that's big enough for this thing. I'd spank her buttocks to make her swing better. He'd do the right thing with his mouth. Let her get used to being a slut.
Well, half-brothers and half-sisters are not related at all, so it can't be considered something bad or immoral. It's no surprise that an adult guy and girl, with no regular sexual partners and almost daily being around each other, suddenly felt attracted on a sexual level to each other. Considering that the girl liked it (the guy then no question), I think they will continue to practice this kind of thing from time to time.