"Isn't it lovely, all alone" to me is about acceptance that you're better off alone "heart made of glass" is about an empathic heart that breaks for everyone's pain and suffering, so they feel the heaviness of it, always. "Mind of stone" is about perserverance, despite all this pain they feel, they haven't given up on life. "Tear me to pieces, skin and bones, hello welcome home" is the familar feeling of pain, since you've had it all your life, familiarity is home but also, they want to suffer in your place, they want to take your pain away unto themselves.