The twin thats younger than me

We were born at the same time, raised in the same house, but we remained different. You barked while I talk, you played with a ball while I played with a doll, yet we still end up the same. We're both curious. But you're the one who went into the road I could not cross. i pull the covers back- your cage is still empty. But my heart is so full of you. Too full of you.