Her life is empty from all of the things that are missing in it. She just wants her life to be whole not empty she misses the things that are empty in her life she doesn't want her life to be empty anymore then it already is.
I watched you die
I heard you cry every night in your sleep
I was so young
You should have known better than to lean on me
You never thought of anyone else
You just saw your pain
And now I cry in the middle of the night
For the same damn thing
She watched him die as she cried. She was so young when he died and she will never want to see it happen again after that day. She heard him cry and it made her think that he could have known better then the choices he had made in the first place. She doesn't care what he does anymore so she hears him cry as she watched him die.
I cannot cry
Because I know that's weakness in your eyes
I'm forced to fake
A smile, a laugh everyday of my life
She can't cry so she pretends that she is happy with her life in less she is truly happy. She wants to be happy but when shes not she pretends to be and she cries when no one is around to see her do so.
Because of you
I never stray too far from the sidewalk
Because of you
I learned to play on the safe side so I don't get hurt
Because of you
I find it hard to trust not only me, but everyone around me
Because of you
I am afraid
She is explaining what she did to keep herself safe from different things in the world to stay protected. She won't stray away from the safe place were she is standing.