He who feeds my fear

My monster is always there.
He knows when I care and toys with my fear.
He pushes harder when I stare,
And when I stumble, he plays it off like we're brothers,
Saying I have to share, so he can scare the others.
He always hides behind my back,
Whispering all the things I lack,
Waiting for me to crack
And let him turn my mind black.
But I can't let him,
'Cause you are the only one,
The one I wish to hear.