After just reading the long description, you badly need an editor. I am cringing. And I think you might mean "Darling" in the title? I'm gonna pass on reading this- but you'll get no thumbs down from me! :)

Rarity is left alone one night and is very tense, Sweetie belle is at a sleepover.

Two complete thoughts, either put a conjunction in between the two parts, or seperate them with a period.

Alone she close shop but her helper came back working on curtien days

Alone needs a comma after it.

Change close to closes.

Put a comma on but.

Change came to comes.

Curtien should be curtain.

Put a period after this, because the next sentence is a complete thought.

trying to think of a way for him to stay she comes up with something

Put comma after she.

So one night when Sweetie went to a Sleepover at Applejack's place.

Dependent clauses should end with a comma.

You already said Sweetie was away in the beginning of this desc.

Disliking the thought of being alone she gets Mirrors to stay for the night. Nightly active happen for the two.

These sentences are poorly worded.

I bet "Mirrors" is a self insert OC for wish fulfillment.

This story is garbage. Get an editor.

5473965 Thanks for the word help.

This was a awesome part it in was sweet and spicy.