This is a nice little story. I won't rehash any of the things that were already hashed out. At least I will try not to do so. As I expected, Muse got to most of the technical aspects of the story right off. She is so damned good at it!

Tis my turn to go through and offer my own brand of commentary, evil as I am.

The silk sheets were cool on her back. She nibbled on her lower lip, pondering, "How long will he make me wait this time?" Probably longer than last time.

The part in red should have been part of her thoughts. Either that or it should have read something to the tune of "He would make her wait longer than last time". The narrator shouldn't "probably" know.

Christine breathed a heavy sigh and craned her neck to try and see the clock. She’d only been waiting 30 minutes.

I would have modified this stylistically. "Craning her neck to see the clock, she breathed a haevy sigh. It had only been thirty minutes.

Do not use contractions in narration. It's bad form - mostly.

She doesn’t mean to be impatient; she was just a spoiled child, with three brothers much older than herself who doted on her every moment.

In this case, due to the conversational sounding narration, the contraction works well. Sometimes you have to abandon the rules. Good job with that here.

The youngest made sure she was tough enough to stand up for herself and be able to fight off all the boys and men who were not as nice as her brothers were.

I would have found a way to shortent his a bit. Maybe even turned it into two sentences. I would have also found a word different than "nice". In this case "nice" is a weak word. Not incorrect, just doesn't fit stylistically.

Suggestion: The youngest made sure she was tough enough to stand up for herself. They felt she ought to be able to fend off men and boys who were not as upstanding as her brothers.

Thank goodness, she thought, when Tom walked in just as her back started to sweat on the sheets.

This is very akward. Also, you need quotes around her thoughts.

Suggestion: Tom walked in, just as her back had begun to sweat against the sheets. "Thank goodness" she thought.

Christine pouted, that meant as she had suspected, her lesson wasn’t finished.

This was akward as well has being technically unsound. I won't hit the technical aspects but I will say that you should have said this in a very different manner.

Suggestion: Christine pouted, suspecting/realizing/understanding/knowing that her lesson was not over.

She loved getting it in both holes, but more waiting for him, and no cumming, she let out quietly, “shit”.

This is about three sentences waiting to bust out. It was akward and I really think you intertwined two different thoughts here and failed to adequately bring them to light. Also, "getting it in both holes" doesn't work here. It is too colloquial. This was a case where common parlance should have been avoided. The sentence is also technically unsound. I don't have a suggestion here as it would have required assumption to determine what you were hoping to get across.

She didn’t know Tom was still there at the door, “Was that a cuss word I heard?”

This should not have been one sentence. Also, "cuss word I heard" makes it sound a bit funny. I would have tried to avoid the rhyme.

She groaned quietly, she would have plenty of time to reminisce, take her mind off what her body will be going through, because she just tripled her punishment

This was not a sound sentence and should have been divided into a couple or three.

Suggestion: She groaned quietly. She would have plenty of time to reminisce and take her mind off of what she would be suffering. She had just tripled her punishment.

I am not trying to rewrite waht you brought here. I am trying to show you a few different ways that might make your tale flow a bit better than it does. One of the things you will notice is that there are times to write concise and short sentences; choppy even. Mainly, it is best to use short and choppy sentences when creating a sense of urgency. It also works well with high action scenes.

The beginning of the story should have been urgent. She was waiting. The time was passing interminably slow. Was he ever going to arrive? Was she ever going to find release?

Short and choppy would have aided that feeling.

When setting a slower or sensuous mood, it is usually best to write more intricate sentences that are drawn out and filled with adjectives. Like when he filled her cavities with one vibrator, followed by another, creating in her a sense of need and longing that she thought would never arrive. She so loved when he would use both of her holes as if she were a toy to be used for his sadistic pleasures. But she would have to wait; wait to find release from the agonizing pleasure she suffered for him.

Okay, I am done. I am also looking forward to your next piece. I suspect it will be even better than this tale. Keep it up.