"Why's everyone so mad at him?"
She slurred.
"Well because he's not here,
and they envy him for that"
I stammered.
"Psssh, why would they envy that?!"
She smiled.
"Simply put,
he moved on with his life,
and everyone here can't"
I sneered
"What about you?
Have you moved on?"
She sang.
"I'm here aren't I?"
I snarled.
I think you need a bit more contrast between the last two "I ____"'s. Snarled is perhaps a bit more intense than sneered, but I don't think they produce very different feels. Personally, I would replace "sneered" with something much weaker (I know your selection of "s" words is limited by now - perhaps "stated" would be enough) to save some punch for that last line.

Anyways, that was probably too many words for such a small point. I dug it. It reminds me of the place where I work.
I like it.

"Success is as dangerous as failure. Hope is as hollow as fear." - from Tao Te Ching