Look at what you've done.

Some day you'll see what you've done to me. Not today, not tomorrow, but the future. It will hold all the secrets of the past. Come slipping out. You'll come undone to nothing, just like me. The secrets, the lies, all of it will come out one day. I hope I'm there to see that day and maybe it'll be okay for a while. I'm trying to keep myself sane, but one day I'll be gone. You'll realize what you've done and you'll feel horrible. I don't know what it's like to be in your shoes, but once you're in mine, oh you'll know. The days go by and I wonder when it'll all get better. I don't regret you, I never would. I'm just like you. You just don't wanna admit it to yourself. We haven't gone through the exact same things, but we've gone through the same amount. I'm trying, as hard as I can. It's just, one day... I'll go insane. Just like you.

helloo!
I'll be your reviewer for today I want to start off with saying that I really like your write. I would put it in another form though if I were you. It will be easier to read.
This is how I would write it:

Some day you'll see what you've done to me.
Not today, not tomorrow, but the future.
It will hold all the secrets of the past.
Come slipping out.
You'll come undone to nothing, just like me.
The secrets, the lies, all of it will come out one day.
I hope I'm there to see that day and maybe it'll be okay for a while.
I'm trying to keep myself sane, but one day I'll be gone.
You'll realize what you've done and you'll feel horrible.
I don't know what it's like to be in your shoes,
but once you're in mine, oh you'll know.
The days go by and I wonder when it'll all get better.
I don't regret you, I never would.
I'm just like you.
You just don't wanna admit it to yourself.
We haven't gone through the exact same things,
but we've gone through the same amount.
I'm trying, as hard as I can.
It's just, one day... I'll go insane.
Just like you.

Other than that: great write! It has a lot of emotions in it!
-qaralynn-

Yaaaah! I cannot stress more that you neeeeeeed to indeeeeeent. Since, though, that qaralynn already covered that, I'll do some more specific nitpicks.

Not today, not tomorrow, but in the future.

Not sure here, but maybe a "They will all come slipping out."

But once you're in mine, oh, you'll know

Also with this one, you seem to be changing perspectives. I think it should by "oh, I'll know" instead of what you've got. I'm just going off the line before it, if you're confused by what I mean.

You just don't want to admit it to yourself.

Normally I wouldn't be picky about this, but "wanna" right before "admit" doesn't sound right and doesn't flow. It's not a matter of vowel-vowel, because "want to" would have the same issue in that case, but a matter of it being the same vowel. "Want to" will give it a nicer flow.

But we've gone through the same amount.

I know, I know, it's not the beginning of a sentance, but unless you want to go off of the structure qaralynn offered (which I wouldn't recommend) it is the beginning of a line. Same with that other one.

This was a really good poem. I enjoyed reading it. Just make sure it looks as much like a poem as it sounds, or it will intimidate readers and make it more diffcult to follow.

Awesome-sauce job!

I really love your style of writing but as it's written it feels too jumbles. I think it would be better read if it were to be in a column. That's just my opinion. I love this poem/piece of writing though. It's so deep and I think alot of people can relate to it.
Keep writing
-Wolfie

I don't know what it's like to be in your shoes, but once you're in mine, oh you'll know.

I really like this line

I love this poem but it really needs some breaks, it's all jumbled together - as qaralynn, Sassykat, and wolfgirl have mentioned. So go through and break it up a bit.
Also you need to make it more elegant. You've got a couple of really blunt words in there that mess up the flow, so go through, find them, and fix them with nice, fancy words! Yay!

Otherwise this is a really great poem and the emotion is very nice. Great job

Keep writing,
Alzora