Very good work.

1940397

Nice cover art / avitar.

I have to agree tho

I pondered down-voting this for some minutes now. And I made up my mind: I won't.
The sleep-over with a confession as a bonus isn't really a 'new' idea. Though that really doesn't mean anything. If you write something that was done a million times before, but you manage to do it good enough, then there's no way I'm going to complain. And I, for one, found the ending quite entertaining. I had a good laugh at that. "Hint hint." Heh.

Now, what made me consider a down-vote:
Your story could use some proofreading. An editor. There are some mistakes here and there, some odd word choices, stuff like that.
Twilight was... waaay to demanding and pushy. She did some things almost against Flutters will. You're balancing on a very thin line towards rape there, only barely managing not to fall into that. It just feels like Twilight is really eager (way to eager, it made me question if I really read something about Twi) and drags poor Fluttershy, who happens to be in love with her too, along. There even was that moment when Flutters snapped and said something along the line of "Shut up" - she didn't hesitate afterwards, she didn't apologize, nothing. Again - that made me wonder if somehow, she was magically changed into not-Fluttershy.
Twilight leading Fluttershy on surely is something that simply has to happen with those two, but I'm missing her reassuring her, showing patience with her, her own share of kindness. I have to decide if that felt rushed or cold-hearted on Twis side - and I don't know which one would be worse.
If you ever played Bioshock, the phrase "would you kindly...?" will just... slap you in the face and pull you out of reading any further for some moments. But that's just a problem of mine, I guess. I don't think that reference was intended, was it?
Those last lines when they talk about their commitment are somewhat depressing. And Twilight trying to comfort Flutters with something along the lines of "you were a really great buck last night and you'll always be a friend" just sounds... wrong. Completely wrong.

To finish my thoughts on this story - it was a nice thing to read that they don't smell like flowers and taste like honey. After a few hundred stories I've read, that's a first. And I like it. I like that Twi can't stand the smell or taste, I like that Fluttershy doesn't find it tasty, but doesn't care much about it ether.

I would try to give you some advice on how to improve this story - in my opinion, of course - but the longer I think about it, the more I tend to say that your characterization of those two is the source of most problems. You had some good ideas though, so, yeah. No down-vote.