This was okay, it was more story-like, than poetic. BUT anyways, let us pick it apart, shall we? :]

"The twilight hour is the darkness hour, yet it's the lightness."
Erm. Maybe instead of "Darkness" and "lightness" (since lightness sound REALLY wrong in my opinion, no offense) you should try "Darkest" and "lightest" :]

"I lie on the grass and watch the sky go from a beautiful pink and blues to a dark ash Grey."
uhm.. try this with the wording, it's a bit mixed up which makes it harder for the reader to read as is.
"I lie on the grass and watch the sky go from beautiful pinks and blues to a dark grey." :]

"I wish he was here to lie here and watch to, but I know he is watching over on the other side of the world."
"I wish he was here to lay here with me, but I know he's doing the same on the other side of the world."

"I lie there and then I fall a sleep and I start to dream. I dream of him and his golden smile."
"I lay there and then fall asleep dreaming of his golden smile."
(All the extra words you put into all these aren't necessary, and it just drags it out more. Sometimes that better, but i think in this case it'd be better shorter, do you notice how I've only changed a few words? even though it looks like a lot, it really isn't.)

"I dream of him on a hill coming to me and then when he does he says to me " Sarah, I don't love you any more. I have fond someone new."
"I dream of him on a hill coming to me when he arrives, he says "Sarah, I don't love you anymore. I have found someone new."

"Then a girl with black hair cames up and starts to kiss him."
"Then a girl with black hair comes up and starts to kiss him."

"I just stand there shocked and broken hearted. I want to wake up but I can't I just try to make him like me again. I watch as you go into the sunset with your new girlfriend and I wake up. I wake up to your sweet smile and I know you will never leave me because you love me."
"I just stand there shocked and broken-hearted. I want to wake up but I can't, I just try to make him like me again. I watch as he goes into the sunset with his new girlfriend and I wake up. I see your sweet smile and I know you would never leave me because you love me."

Well. There we go. I think that's good. :]
(Though.. this is still a lot more like a short-story than a poem, just so you know.)
5/5

This could be a good prose. I'd suggest if you want to make it a prose break it up into 3 or 4 groups of a few sentences. If you'd like to make it more poem formatted try this:

POEM STYLE:

[The twilight hour is the darkness hour,
yet it is the lightness **

I lie on the grass, watching the sky
go from beautiful pinks and blues,
to dark ash grey

I wish he were here,
to lay and watch with me.**
But, I know he's watching over
from the other side of the world

And, I lay there falling asleep,**
and I start to dream -

I dream of him and his golden smile,
I dream of him on a hill, running up to me
... and then when he does he says to me,
"Sarah, I don't love you anymore, I've FOUND someone new." **

Then a girl with black hair COMES up, **
and she starts to kiss him.
I just stand there shocked and broken hearted

I want to wake up, but I can't
I just try to make him like me again.

... I watch as you go into the sunset,
with your new girlfriend ...
and then I wake up. **

I wake up to your sweet smile
and I know that you'll never leave me**
because you love me.]

You have a decent poem here, Sarah. It's something you do have to work at but you have talent. I'd suggest looking over the changes through-out the poem style that I changed and thinking them over. A few spelling errors and other areas just weren't working well with the piece. They were throwing it off, messing with the flow and everything. It wasn't working out. BUT, with a few tweaks any poem can be fixed.