You give her a show.

Now that you know this, even the last drop of guilt leaves your heart and mind. If Vivian wants to watch, the least you can do is give her a good show.

You confidently return Shelly’s embrace, holding her tightly and pressing her deliciously sexy body against yours. With one hand on the nape of her neck, you pull her closer, deepening the kiss as you devour each other’s mouths, tongues wrestling for power. This is the first kiss you’ve had in weeks with her! You make out like long lost lovers. Your other hand moves to her back and slowly descends until you reach her succulent ass, giving it a hard squeeze.

Shelly has a hand on your hair, messing it in the heat of the kiss while she sneaks the other one under your shirt, caressing your bare chest.

Your moans are loud and hungry. You break the kiss to catch your breath and steal a quick glance to Vivian. Her breathing is fast and she’s slowly playing with one of her breasts as the other hand fondles her pussy over her pants. Her eyes are completely glued to you and your sister.

Relieved and absolutely ecstatic that you were right, your mind races, thinking of ways to both give Vivian the best show possible and please your hungry sister.

You pull Shelly’s T-shirt up and her bra down, revealing to you and to Vivian the enormous pair of melons. You put one nipple in your mouth and suck on it as hard as you can while your hand plays with the other.

Shelly grins widely, enjoying your touch.

“Yes, little brother. Suck on your big sister’s tits! Enjoy them as much as you want!” Shelly purrs, running her hands through your hair lovingly.

It seems that Vivian’s legs began to grow weak, because she had to sit on your desk chair.

“Mmmh! Sit down!” Shelly commands. You comply and sit on the bed. She helps you take your pants and boxers off, revealing your painfully hard cock.

“My little brother’s cock…!” Shelly beams. “My little brother’s magnificent cock!”

Kneeling, she angles herself in order to give Vivian a good view of your dick, showing she’s also aware of your girlfriend’s… new fetish. She plants soft, slow kisses allong your length, then settles her lips at the head of your cock and licks in circular motions before finally taking you whole. Her head bobs up and down as she masterfully devours your dick.

You look at Vivian, whose eyes can’t seem to leave your shaft, but notices you looking her way and flinches. You smile at her encouragingly and beckon her close.

Vivian hesitates, but slowly stands up, then sits besides you on the bed, now with a perfect view of Shelly’s blowjob. You kiss Vivian tenderly, and she accepts it, holding your hand as your tongue explores the inside of her mouth.

“Does that feel good?” Vivian asks you, breaking the kiss and looking as your cock goes in and out of Shelly’s mouth.

“Yeah. Shelly’s really good.” You answer.

“Would you… teach me how to do that, Shelly?”

Shelly stops the blowjob to give Vivian a bright smile. “Of course! It’s not hard to do, you just need practice. Look, here’s your first lesson.” She says, going back to your cock. “Mix it up, don’t just do the same thing over and over. That’s boring. You can take it in you mouth, sure.” She says and does just that, sucking on your cock as her head bobs. “But after doing that a few times,” She says, catching her breath. “do something else. For example, John loves it when I do this.” Shelly gives you a long, hard lick that goes from the base of your cock to the head. She does it a couple more times before her tongue settles at the tip, swirling around it. It sends shivers through your body.

All the while, Vivian nods attentively.

“Practice enough, and one day you’ll be able to do this.” Shelly begins to swallow you whole, taking your length completely in her mouth and into her throat. Vivian gasps at the sight.

“S-Shelly!” You say, warning her, but she either doesn’t listen or doesn’t care.

She stays there as you unload your fill into her mouth and down her throat. You can hear her audibly swallowing and her throat expands and contracts as she does.

She smiles, eyes closed, and gives a delighted moan, relishing the sensation and taking in the reality of the situation. You can hardly believe this yourself. Your girlfriend is holding your hand tightly, watching as your sister swallows your cum.

You turn your head to Vivian, and she gives you’re a shy, embarrassed smile when she notices you staring at her.

“Did you like that?” You whisper in her ear, your voce as neutral and comforting as you can manage.

Vivian nods slowly with a small smile. “Yeah, I did. It was… very hot, in a way.” Her face is still bright red and her breathing is heavy. “Could I… watch some more?”