Ok, your arrangement needs work and I have provided a suggestion for this so... if you don't like my suggested format, just ignore it, but I have altered the errors of capitalisation and other punctuation throughout this. Feel free to alter this suggestion as you wish, just quickly altered your original format:

That feeling in my chest
when I see you can't be controlled.

I get the best feeling in the world
when you say hi or bye to me, or even smile,
because I know even if,
just for a split second,
I've crossed your mind
that makes me grow fonder
of you each and every day.

So here I am writing this to you
to express what I cannot say to you in person.
I wish you could hear every word I write on this paper.

I've waited too long to tell you
and now you've moved on.
I don't understand, explain to me
how you have all the time in the world
to go out of your way and
make other girls that don't know you
as well as I know you
fall in love with you,
but you don't have enough time
to pay attention to the girl who already is.

The same girl,
that's been with you through every storm,
that same girl,
who let you cry on her shoulder,
when those same girls you go out of your way,
and get them to love you,
break your heart.
No matter what happens
I'll always be there for you.

Just promise me you won't forget me,
promise you won't stop saying hi
or giving me that smile in the hallways
because I look forward to those,
they make my day.

You will never understand my pain
until your heart's been broken,
just like mine has been.
My Heart is not the only thing broken,
my soul is too.
The pain is unbearable.
I can't help but want to cry;
cry until I can't breathe
until my lungs give out.

The worst way to miss someone
is when they are right beside you
and you're wondering if
they miss you the way you miss them.

I'm standing right next to you looking at you
and hoping you get a clue
and yet you don't.

The insane thing is
I miss you like crazy.
I can honestly say I'm officially missing you.
Hopefully I'll be able to pick up and heal the shattered pieces
of what's left of my heart
but I'm not sure that's even possible
because in order to put it back together
I'll need all the pieces I left of those pieces where we stood
when you gave me that devastating news...

Besides all that - I really like this piece. Love your raw emotion and honesty. 5/5

Oh, and welcome to PnQ. (: