See that girl beside you? You think of her as your best friend right? She's the one who had always been there for you since the day you met her. 
You practically grew up together and so youre confident you know everything about her.
That's where you're wrong.
That girl in front of you? She's hurt. She's mad. She's depressed. Most of all... She hates her self.
Smiling, laughing... All those verbs fit her perfectly as you know her to be an easy going person, and someone who seemed to be contented and happy with the way her life is right now.
Again...youre wrong.
Learn to look past the physical... You said you knew her...youre a liar.
That same girl, she goes home finding nothing but the feeling of emptiness. As if no one was there for her, yet she believed that you... You will be there for her no matter what.
But where were you when she needed you the most?
The day you told her "I have a girlfriend", she smiled at you, caressed your hands and told you, "I'm very happy for you". You hugged her and told her that you were the happiest man alive. You saw her laugh and punched you for your silliness like the usual, but you probably noticed something different. Her smile seemed forced and you questioned yourself and her for it.
"I'm just tired", this was her answer, and so you ruffled her hair telling her to go home and get a good nights sleep.
Idiot. Bastard. When she said she was tired... She was tired of living. Tired of being unnoticed... Tired of you.
How can you be so dense? Fool.
That one girl had always tolerated you and your never ending frustrations about life
That girl supported you all throughout your failures and successes 
That girl... Your best friend... She was there when you first told her that you were in love.
What hurts most is that she endured it all... Without you noticing her struggle
As you rejoiced for finally getting the girl you longed for... The girl who had always been there rejoiced too... But you're clueless.
That girl rejoiced? Think again.
You should've ran after her when she said she was tired. You should've taken off her smiling mask.
That one girl...she's hiding something. 
Your a liar for saying you know everything about her... But she also resembles one, for making YOU think you do.