In 2003 I was facing the summer between my sophomore and junior year at college. It was an exciting time for me, made more so by my incredible girlfriend Gwen. She had it all: five foot six with golden tresses that had just a hint of a natural curl about them, a light tan that showed she laid out in a thong (thank god for backyard pools) and a faultlessly sculpted ass - I loved the way her cheeks swelled into a perfect upside-down heart. Then top it off with deep brown eyes, a wicked sense of humor and a playful mind that always kept me guessing. I thought it was easy to see why I had fallen for her.

We had been hot and heavy for six months since she was on campus for a pre-frosh weekend and we hit it off over a bottle of cheap wine in my dorm room. That night we hooked up for the first time after kicking my roommate out for the duration. She told me she had been fantasizing about me for years. Fortunately reality lived up to fantasy, and we have been going strong ever since.

Of course it was a bit weird to be getting hot and heavy with my little sister's best friend, but love and lust does strange things.

The hardest part for me was, as I got closer to Gwen, I started to notice how Robin had also transitioned from a gawky, awkward younger sister to a tight eighteen year-old, with a killer little figure and dazzling smile. Robin's bright green eyes, and finely-boned features, which had taken the place of chubby cheeks and librarian glasses, made me acknowledge that she was becoming a woman. She grew her chestnut hair long, which Gwen loved to brush as they had "girl time" during sleepovers. Being best friends since they were in grade school they were quite 'sisterly' - meaning, of course, they discussed girly things together which I had neither knowledge of, nor interest in.

Now I know it is weird for a brother to be checking out his little sister like that, but she was undeniably hot, even before things changed for us. And the start of those changes happened that night over ten years ago.

On the night in question, I was home for the summer and our parents were out at a wedding and not due back 'til Sunday. Robin was at a party and she was under her usual midnight curfew. Gwen had skipped out of the party early to come have some sexy fun time with me.

By ten o'clock, Gwen and I had drunk a couple of beers liberated from Dad's party supply, and we were watching a little TV and feeling frisky. With a few hours to spare, I reckoned on getting some of my girl's hot delights before Robin came home.

I had been rubbing her shoulders and decided it was time to make a move with some light kisses on her neck and nibbling her ears - a favorite of hers. With the alcohol rushing around with our hormones we were in an energetic mood and up for a bit of deviant behavior.

Gwen leaned back and we kissed, softly at first and then with more fire. My hands had long since drifted down from her shoulders to caress her torso, and my long fingers were pulling on her thick nipples through her shirt when she pulled away saying, "stop, we can't - not here - someone might come in." I knew she was playing because we had fooled around in much more public places than my parents' couch. I grabbed at her again and she jumped up running for the back of the house giggling like a, well, like a school girl. I leapt to the chase.

We dashed from room to room. Sometimes she was laughing as she ran down the hall. Other times she would hide in the darkness before ducking out of a door I just entered, silent as a shadow. When I reached my parent's room I turned on the lights. She popped up from behind the bed and tried to slip by me, but I tackled her and pinned her down on my parents' bed. "You've caught me." She said while her taut breast heaved against me. "Now what are you planning to do to me."

"Oh no! I'm the winner; it is you who are YOU going to do for ME."

"Yeah, okay. What do you want? A BJ?"

"Hmmm." I pondered rolling off her. "I got it. Strip for me ... here in my parents' bedroom with the curtains open and all the lights on."

Since my folks hadn't bothered to close the blinds before they left, the dark windows reflected our shadowy selves back at us as we rolled around the bed, the overhead and wall lights glowing against the ebony night outside. The room looked out onto the back yard so there was no passing traffic - a bit of a disappointment to me. I'll admit the thrill of her stripping before an audience had an appeal.

Gwen hesitated, and looked from the window to me with a challenging glare as I silently watched her process the idea. She bit her lower lip and stated emphatically, "Fine, I'll do it. But you better give me some incentive. Whip it out and show me you like what you are seeing. Let me watch you jerk-off while I dance."

My first thought was no problem; I'd been doing that for years now. But I was a bit apprehensive. I hadn't really done anything like that with her - I know we'd been dating for awhile, but our sex was mostly straightforward; the only time she'd ever seen me jerk myself was finishing off after I'd pulled out of her.

"I didn't know you liked that," I said undoing my belt with a smile.

"Sometimes..." was all she said, looking coy.

"You should have told me sooner."

"Oh, shut up and get hot." She then gave me a hell of a buzz by flicking on the bedside lamps. The extra illumination made everything a lot brighter, clearer and real. I suddenly stiffened up pretty quick.

Gwen flipped the satellite radio on Dad's stereo to some bluesy music channel and began to undress to the rhythm of the music. The bottom button, then another opened on her tight flower-top, revealing her creamy sun touched skin stretched across her flat stomach. As the rest of her buttons followed, I held my breath in anticipation.

Like Clark Kent ripping open his shirt to become Superman - Gwen baring her chest usually signaled her transition from demure playful girlfriend to roaring sex kitten. She moved slowly, rolling her ass in her tight jeans, as the top button went with one hand while stroking her body with the other.

Her beautiful breasts stood out proudly, capped by those pink puffy hard nipples. I loved her breast even if she complained they were too small. My favorite thing was the way her cone shaped nipples jutted out like Hershey Kisses on top of a pair of cupcakes. They were super sensitive too, arousing her sometimes just by the feel of a shirt rubbing against them. Gwen was usually embarrassed about them, but when she was horny she'd display them proudly; like she was then, rolling each between her fingers, smiling a wicked smile at me.

I was transfixed, watching the light play on her well sculpted torso. She snapped me out of it when she stopped moving, and said, "Come on, drooler ... show me yours."

I laughed as I finished undoing my belt and unzipped enough to get my own jeans down, got muddled, then decided what the hell and kicked off my sneakers, socks and shoved off both my jeans and underwear in one push planting my bare butt on my parents' bedspread. I sat back against the headboard, Ramones t-shirt up over my stomach, dick pointing rock solid up at the ceiling.

"Wow" Gwen said, both joking and serious. She had seen my eight inches often enough, but she really seemed to dig it. I ran a finger up the side, tracing one of the throbbing blue veins, to the mushroom tip, and spread the clear drop of pre-cum over the rosy flesh. I saw her eyes were glazed over; no result of alcohol. This girl was getting seriously horned-up.

Gwen looked from my dick to my eyes, still waiting. I grinned and grabbed the base of my shaft and slowly started to pump my fist up and down. Gwen made a little moan and started to dance again. She was getting into it, swaying and spinning, dropping into a crouch only to pump her hips back into the air as she stood up. She was facing away from me when she undid her waist button and slipped a hand down into her panties.

"Cheater," I smiled, loving every minute as she drifted further into her sexual fugue. I'd never seen her so damn hot. Then I thought I glimpsed something past her, at the window. I never actually saw an identifiable object, but just the shift in light against the dark glaze caught my attention behind Gwen. I looked again - nothing - and then Gwen swayed in front of my view as she danced. I turned my attentions back to her as she kicked her sandals at me, laughing, pointing at my cock to remind me that I'd stopped tugging, distracted momentarily. She turned away from me and wiggled out of her jeans flashing that ass I love so much. Gwen looked back at me through the V of her legs as I pumped my pud spreading the shine of pre cum over my swollen cock head.

"Oooh. Your - cock - it's turning purple. Are you going to blow?"

"No. It's just letting you know it likes what it is seeing."

"Let it see this," Gwen said hopping on the bed, shaking her panty-clad butt cheeks at my face. She brought them close enough that I could smell her sex, then scooted down so her firm cheeks rubbed on my cock. I think she got as much of a sizzle from that contact as I did - she shuddered in excitement and drew away as I tried to pull her onto it. Then she danced over me in only her white high cut panties, one hand down the front. I did my duty and jerked, careful not to push too close to the edge. I actually heard Gwen's fingers squish into her pussy as she moaned and then said, "Oh fuck ... I need these off."

She dropped her panties - no standing on ceremony - and stood still over me, feet planted on either side of my thighs. Along with her ass, Gwen's pussy was on my top ten list of favorite things in this world; tight, wet and welcoming, what's not to love. At first she'd had a light downy blond bush but had come to favor shaving to a small landing strip in deference to my love of going down on her. That night, her normally neat, smooth, bald cunny â€"by day just a childlike slit between her thighs - was swollen for fun. Her outer labia open enough under their own excitement to allow me a view of her glistening inner lips protruding and her small clit peeking out of its hood. She had spread her juices over her delicate flesh and she could not resist opening up like a flower with her fingers and asking me in a breathless moan, "You like?"

Stupid question. I wanted to bury my face in it. But as I leaned forward she drew back and groaned, "Pull that cock..."

Language like that was not usual either. I guess the sexy dance and exhibition had gotten to her. It certainly brought no complaints from me. I did as asked and she fairly pounded her pussy with her fingers. I always imagined her masturbation might be a gentle exercise with candles and soft music, but here she was standing before me, unashamedly spreading her pussy lips with one hand and thrusting juicy fingers in and out with the other while rubbing her clit intermittently with her thumb. It was all I could do to keep from cumming, but she didn't even try. Gwen yelped, and dropping to her knees over my legs as her orgasm took her. That's when I got the shock of my life. The window. A face. Definitely; just a white orb in the black night. But recognizable: Robin. I gasped, but it was lost in Gwen's cries of ecstasy.

I stopped jerking my cock, eyes fixed on Robin's. She'd met my gaze with her own wide eyed stare and we were both like rabbits in headlights. To this day I'll never forget the tumult of emotions on her face; shock, guilt, and definitely curiosity, bordering on fascination/lust. About that time Gwen doubled over and sucked my cock into her mouth.

Not surprisingly, I blinked, looked down at Gwen's lovely bow shaped lips stretched around my cock and blonde head bobbing up and down - I mean, who wouldn't - and when I looked back, Robin was gone from the window. I only saw my own reflection in a faded dimension, with the dark reflection of Gwen's superbly sculpted butt hovering beneath it. Not a bad view at all.

I was breathing heavily, shock having the dual effect of adding to the horniness and also distracting my mind from the desire to cum. In fact, after I'd reconciled what I'd just seen with some vague sense of morality, I decided it was a GOOD thing and thought what the hell, it will teach her to peep in windows.

I pulled Gwen up and made her clamber - willingly - onto my solid erection. She was so wet that she sank down on my long tool, not stopping until I was fully sheathed in her embrace. I took my t-shirt off so I was as naked as her. She didn't so much bounce up and down on me as frantically grind her clit back and forth against my pubic bone. She was so wet her juices were flooding down over my balls onto the bedspread. I worried about stains on my parent's comforter, but only for a fleeting second.

I grabbed her ass with both hands, a flexing cheek cradled in each palm, and began to join her rhythm. My mouth alternated between each nipple as Gwen thrust her smooth breasts across my face. Each bud was like rubber; flexible and chewy. My attentions sent spasms of pleasure down her body. She started to cum and cum again, thrashing atop me. The smell of her hot flesh, her sex juices and her gorgeous banner of golden hair as it caressed my face was overwhelming; I knew I couldn't hold out much longer. I told her so in gasps and she groaned back that I should get on top and finish off both her and me.

I flipped her round, slipping out of her as I got her laying on her back on the bed. We scooched to the edge and I stepped down to the floor. Cradling her calves in each of my elbows I spread her wide and sank back into her delicious depths. Plunging into that tight, sweet pussy, gazing down at her blushing tits and beautiful face creased in orgasmic delight was an unforgettable experience, heightened by the thought Robin could still be watching at the window. I glanced around, hoping to find her enthralled by my thrusting buttocks but there was only the night looking in. Robin was in the room.