Stop and make sure she's ok.

You turn as you hear your sister step out into the corridor, mouth opening to greet her, already trying to come up with some way to explain to her what you've seen, what's happened to you -

But as she comes into view, your mouth can only hang open dumbly.

Your sister's only a few years younger than you; this past year she started the same college as you, but she's often mistaken for a girl still at the tail-end of high school. She's always been pretty, even after she started going for a gothier look and began dying the light brown hair she shared with you black and started wearing cobwebbed patterns, laced sleeves, and nothing brighter than a dark grey. And she didn't, in a comparison you'd never thought to make before, look like a slut.

This girl does.

A black tank top does its best to contain a pair of tits as big as her head. That's cocked on one side, your sister's heavily made-up face beaming across at you as her pigtailed black hair dances a little as she shifts from side to side. Her face is flushed; with a twitch you realise as you look down at the pair of frilly black panties that are all she's wearing below the waist that the reason for that is that she's currently got one hand stuck down them, fingers moving beneath the material.

"J-Jenny?"

Your sister grins. "Hey, Taylor! How come you're home from classes so early? I thought you said you weren't back 'til later?" You sigh thankfully as she pulls her hand out of her panties as she walks over to you, only to realise the warm hug she gives you only has one arm wrapped around your neck. The other trails down your back to cup your ass, and with a giggle the girl that used to be your sister gives it a firm squeeze. You feel hard, pointed nipples pressing into your chest, and even with the madness of the day so far it's a few seconds before you register it and push her away. "Jenny, what... what the hell's going on?!?"

"What d'ya mean?" Pulling back with a little pout, your sister places her hands on her hips. "What's going on?"

Her innocent response is almost all you can take. "I mean, why the hell do you look like that?!"

"How I look? What's wrong with how I look?" Running her hands up and down her body, sliding over her voluptuous curves, Jenny licks her lips. It looks like less of a check and more a prelude to a lapdance. "Do you mean the panties? Sorry, you know I can never be bothered putting anything back on after Charlie fucks me. I can go throw something on, if it really bothers you."

"No! I mean, yes!" You know, Charlie, sure, they've been dating for years, but Jenny was always planning on saving herself for marriage. "You've... you've been... with him?"

"Fucking?" Your sister looks at you quizzically. "Suuuuure... you know I have? You were just being a total bitch and complaining last night about the noise we were making. So, come on, I had to make it up to him and have him over today for another go." She wriggles a little in place, sighing contentedly. "I was so **** for it, I can't even tell you."

"But.... but....."

"What is up with you today? Honestly, you look like you just saw a ghost." The look on her face of worry must match what your own, but after a second or so it dissolves into an understanding smile. "Oh, I get it. You're jealous. Look, I told you, you're free to get fucked by him any time you want, I really don't mind. We can share." Her eyelids droop and her smile widens, showing a little teeth. The voice that comes out next is sultry, smooth. "We can even share at the same time... if you want..."

For you that's the final straw. You push past her, and sprint down the corridor to your room, slamming the door behind you. Your sister's muffled voice through the door sound hurt. "Oh, fine, see if I help you out again." You don't dare to move away from the door until you hear her light steps moving away again.