What is wrong with him?

A subject pronoun (he) cannot follow a preposition.

He has a new girl friend.
Though I have never been his, I am angry with this.
Why did that happen?
Am I wrong to feel this way?
Why do I admire him?
Is it worth doing so?
I want to scream out loud.

Since I was young, in grade 2 at primary school, I have known him.
He was so charming, but I was not brave enough to tell him.
Now, newbie someone new has come along.

Newbie is more or less internet slang.
There's no chance any more.
I'm just... just complain it venting. 

Complain about it is the correct grammar, but venting is probably what you mean.
I have never dared to imagine to actually being his girl.

OK. I'd better shut up.
Love is not everything. Shut up!

What is wrong with him?

He has a new girl friend. 

Though I have never been his, I am angry with this.
Why does that happen?
Am I wrong?
Why do I admire him?
Is it worth doing so?
I want to shout out loud.

Since I was young in grade 2 at primary school. I have known him.
He was so charming.
But I was not brave enough to tell him.
Now, newbie has come.
No chance any more.
I just. just complain about it.
I never dare to imagine to be being his girl.

OK. I'd better shut up.
Love is not everything. Shut up!