You played her like an instrument

You turned and stepped in front of her, slowly taking in her body with your eyes. She looked at your face, then her eyes lowered to your stiff cock.
"You like what you see, don't you?" you asked and began to trace a fingertip over her chest, between her breasts and rested just above her navel. Your gaze moved from her trimmed patch up to her face and she nodded. You looked sternly at her, "Rub yourself, Lisa."
She leaned back supporting herself with one arm, while she reached between her legs with the other. She slipped her finger between her folds and dragged it up to her clit. She began to rub it in circles and moaned quickly after. You nodded in approval and stroked your cock with your hand.
"Quicker," you commanded, "but do not come!"
She increased her pace and panted heavily between moans. Her arousal climbed quickly and she bit her lip to prevent herself from climaxing. Her eyes started to flutter from the intense pleasure.
"Stop!" you said as you noticed how close she was, "Spread your legs for me, Lisa."
Reluctantly she lifted her finger and looked at you with lust in her eyes as she slowly spread her legs.
You positioned yourself on your knees and looked up at her as you slowly brought your tongue to her clit. "Beg me to lick you," you ordered.

She looked at you pleading and panting heavily, "Please, lick me, professor."
You spread your hand with light pressure on her belly while holding your cock into the other. Your tongue started to circle around and against her nub. She threw her head back moaning and brought her free hand to her nipple and began to rub it. Her hips began to move under your tongue and you pressed your hand down on her belly. Your other hand occasionally stroked your cock to keep it stiff.
"No, Lisa, don't move and don't come," you ordered and hovered with your mouth over her clit slowly releasing some of the pressure of your hand.
She nodded with a longing moan, "I... I can't help it."
"Yes, you can. If you don't follow my demands, I'll let you fail my class, Lisa," you said sternly.
Her eyes widened for a moment, then closed as you placed your mouth over her clit and swirled your tongue again. You paid close attention to the movements under your hand on her belly. Slowing down as you felt her tension rise and speeding up as she began to relax. Her breathing became ragged between moans, but you continued relentlessly. Her body began to quiver and you stopped, lifting your mouth from her sex and you looked at her. Her eyes fluttered, her breathing was ragged between gasps for air.

She looked back at you pleading and begged, "Please, let me come."
You shook your head, "Not yet." You stood up and back and pointed to the floor, "On your knees, Lisa."
You watched her as she climbed off the desk, her legs trembling as she unsteadily lowered herself to her knees. You moved and positioned your cock in front of her mouth, "Beg me to suck it, Lisa, and slowly, very slowly rub yourself, but do not come!"
She looked up at you and with a hoarse voice she started to beg, "Please, may I suck your cock, professor?"
"You're a very good girl, Lisa," you grinned, "now suck it."
She parted her lips and sunk her mouth onto your cock. Her hand went between her legs and held it there, while her mouth moved back and forwards on your shaft. Her other hand held her steady on your back.
You leaned sideways to look down and grunted, "Rub, Lisa!"
She gulped on your cock and began to rub herself, moaning on your cock. You moaned in delight as her moans sent vibrations through your shaft along the pleasure of her hot moist moving mouth.

"Yes, that's it. Now a little faster," you ordered.
She moved her mouth faster on your cock, shuddering from her own rubbing. You placed your hand on her head and entwined your fingers into her hair then pushed her head further onto your shaft. Her gag reflex kicked in and you pulled her back holding her still for a second. Again you pushed her back onto your shaft until she began to gag. Slowly you pulled her head back and began to fuck her mouth moving her head, keeping it shallow enough not to make her gag again.
Suddenly you groaned, "Stop!" and pulled your cock out of her mouth, gave it a few strokes. She saw the throbs and twitches and closed her eyes. Jets of hot cum splattered on her face as you moaned, "Come for me, now!"
She increased her rubs and climaxed shuddering, her back arching and falling as the waves of her climax crashed through her. She licked her lips between gasps for breaths and moans.
"Very good, Lisa, tell me you're my very good girl," you commanded and grinned at the sight of her cum stained face.
She tried to catch her breath and in the haze of her climax she replied with a hoarse voice, "I'm your very good girl," arching her back again as another wave coursed through her.
You murmured, "Yes, my very good girl. You are going to come to me for another practical application after the next lecture." It wasn't a question, it was an order. She could only nod, still not fully back to her senses. You snapped your fingers and pointed at her panties, "Give them to me."
She picked them up with a slightly trembling hand and gave them to you. You used her panties to clean your cock, threw them back at her, then pulled up your boxers and jeans and buttoned up.
"That was very good, Lisa, I'm certain that you're enjoying the release of endorphins intensely." You turned towards the door, "Make sure there are no stains on the desk or floor before you go, Lisa. See you at my next lecture." After that you stepped out of your office and pulled the door shut behind you.

She was stunned from your words and shocked at the realisation that you'd used her as a toy or rather played her like an instrument. She wiped your cum off her face with her panties, then put them into her bag. Tears rolled from her eyes as she started to dress herself. She had conflicting feelings, it was great, really great. But she also felt used, very used. Yet, somehow she liked that too.