"I gave him my love,
I gave him my trust,
But he chose her,
The girl filled with lust."

Good opening and rhyme, simple yet meaningful.

"He chose the Barbie doll,
the perfect little toy,
and there he was,
a perfect little boy"

Second line: Capitalize the "t" in "the"

Third line: Capitalize the "a" in "and"

Fourth line: Capitalize the "a"

Fourth line: Place a period after "boy".

"She was so plastic,
so fake and so dull,
the prettiest little Barbie,
the one you buy at a mall"

Do the same capitalizing as I stated above, just because "She" is capitalized, the others should be too. Make this change on the next couple of stanza's too please. There was no rhyming here, the pattern was lost, which threw me off. Also, the repetition of "so" really ruined it for me too. I think this stanza could be a lot stronger.

Fourth line: Place a period after "mall".

"To hear he loved her,
was pain to my ears,
the thought of them together,
just made more tears"

Good stanza, simply stated. Nice rhyme!
Period after "tears".

"He left me scattered,
on the broken floor.
He threw me away,
for just a little more."

Flawless flow here, this reads nicely! :P

"He broke my heart,
just like that
he used me like
he would use a mat"

Okay, I was very disappointed in this stanza, it was very weak and not full of that many emotions. And he used you like a mat? I'm sorry, but that doesn't make much sense or read well. Try replacing that word with another one that rhymes with "that". I thought here, and in other parts of your poem you could add more imagery and descriptions, but that was just me.

3/5 from me, my suggestion is to just go back and work on this a bit. Take care and God Bless!

He was so perfect
But that was the past
Now look at him
A social outcast