Okay

'I don't know whats wrong with me
Cuz I love him with all of my heart
But then there is him, my only weakness
And inside it tears me apart'

Get rid of 'cuz', because it doesn't fit very well, it sounds quite clumsy and looks ugly on the page, and if you want the reader to empathise, using colloquialisms and things won't help. A whole word can destroy a single stanza so watch out for that :]. The rest of the stanza IS good, sorry If I seemed harsh.

'Talking to him now I hate his girlfriend
Like that of a stupid high school crush
I'm an adult, I'm almost 21
But when I talk to him I still get a rush'

If you're trying to sound phonetic, it's working, the use of 'like', and 'hate his girflriend', is very high school talk. There was a simile here though, so well done.

'He says he has not talked to me
Because he was afraid of what he'd do
He says that somehow I tempt him
And to her he couldn't really be true'

Don't force that rhyme in the last line because nobody speaks like that, in way of grammar, but you could get away with it if you just put a comma after 'her'.

'Like a little kid I wonder who she is
Is she pretty is she nice is she smart
Even though deep down I shouldn't care
Cuz there is a boy who already has my heart'

Good simile, I like this stanza, except you're missing the question marks out on the second line, but if that's intentional, then I apologise.

'I don't love him, I should not care
I've got my relationship, he's got his
I don't know why I'm sitting here thinking
About him and I and this.... '

Sometimes we all think about things that mean a lot to us to later find out that it's stupid and we shouldn't wreck our heads thinking about it. I liked the poem, don't get me wrong, just try to take on board the suggestions I have made, even if you don't change it.

Good work

I like this it was good i think you should name it weakness