I enjoyed this a lot!
The breaks to flash back felt perfectly timed and helped give a reason to the next action more than because that's the story.
Very well done.

If Spike had a 10 inch cock Button must have been rocking a foot long schlong,

9817178
Thank you for your praise and for reading the story, I appreciate it and am glad I could make something enjoyable out of a concept I myself never really gave thought to before.

9817201
I was more aiming for the fact Sweetie, for this story at least, was just a uh... Well for lack of nicer phrasing, harlot.

Assistant.

9817233
Yep.

Wow, Trixie's really digging herself a hole in this one, more so than usual.

Nice, very nice.

"Trixie's idea is so weird and perverted it just might work. If I can relieve the stress on his mind with my body then... Dammit, I'll do it! Whatever it takes to get Spike back to his normal self!" She said as she shot up from her seat, "Tomorrow, I'll fuck the negativity out of Spike!" She proclaimed as the room went silent save for Trixie's smug proclamation of 'I'm a genius' before getting swatted over the head by Starlight. "Now there's only one problem..." Twilight said as her face flushed red, "How does sex work?"

Truly touching. Most excellent.

I overall liked the story and idea, but the pacing was off for me and there was a severe lack of details and 'feelings' during the sex scene. What did it feel like to have sex her first time despite the pain of deflouration? How did Spike feel, being inside a virgin's pussy, and his adoptive sister's at that? How about some details about their orgasms? Not to insult, but this felt almost more like a synopsis than a fleshed-out story in those respects.

There were also a number of misspellings or awkward grammar uses throughout. Now, I'm an author too and know how these kind of mistakes slip through even after proofreading it several times, and this is not me trying to make you mad or put you down, this is purely constructive criticism. Also, pretty sure you messed up the italics in a couple places, listed below:

From

Spike dazedly removed his hands from his eyes and shook his head.

to

Seeing how he'd reacted to the TrixiePie method, she decided to move onto the method stated by Rainbiw Dash.

are italicized, and they're set in modern time, so I don't think that paragraph is intended. Also, 'Rainbow' is misspelled.

This happened again at:

She looked down to Spike who quickly turned to face away from her before she hugged him close, holding him tight as she spoke, "I'm sorry... I'm so,

Best of luck with your future writing endeavors!

~Legion

Not bad man.

"That 'slut' is my little sister!"

Rarity don't get me wrong but you ever looked in the mirror and tell yourself that?

Its would have been nice if there was a chapter where Sweetie showed up to ask for fogginess but Spike shows her that he has a better girl now and her cheating on him was the best thing to happen to him