Starlight glowered. "There you are, you little pervert," she said.

Wasn't it you who had left the door open? Maybe even deliberately?

"Oh, don't you worry," she said, in a tone that told him he should definitely worry, "I'm not going to do anything, about this."
"R-really?" Hope swelled in his chest.
"Nope!" she said, cheerfully. "Now Twilight, on the other hoof..."
"NO!" he yelled, "please don't tell Twilight."
"And why shouldn't I? Why shouldn't I tell her that her precious little assistant is a pervert?" she said.

Alternate ending:
*one explanation by Starlight later*
Starlight: "So, that's what happened."
Twilight: "I see. Spike, there is only one appropriate thing I can do to you now."
Spike: *gulb*
*Twilight kneels down and looks Spike straight in the eyes*
Twilight: "I'm so proud of you, Spike. Carry on."

Good story!
I enjoyed reading it.

Found two small typos:

He carefully, quietly as he could stepped back from the door.

Better: "As carefully and quietly as he could he stepped back from the door."

give you a reeal good look.

That should either be "real" or "reeeal". (In my humble opinion.)

Other suggestion: maybe you should look for an cover-art. Far too many users literally judge by the artwork whether or not they should read a story.

Me: "I feel like reading a fan fic tonight"
Finds a good featured story to read.
My hands accidentally drags the title of this story and puts it in a new tab.
Also Me: "You'll like this story. Your waifu has sex in it"

I don't know if this was a coincidence or not but my body knows what's better than I do. I wasn't planning on reading this story tonight.

What a good fic. I enjoyed it.

I love a good Starlight x Spike story.

Nice fic.

I hope that sequel comes out soon cause he's got a lot of stuff to be let out.

Next time on MLP the sequel to a really nice fic.

xDDD Most excellent.

"And why shouldn't I? Why shouldn't I tell her that her precious little assistant is a pervert?" she said.

Because you´re the one who masturbated.(Smirks) Okay I´m gonna go hide now before she burns my hair off.

8420959
To be fair, it was a small crack in the door, and I don´t think you´d like being watched masturbating regardless.