It's about abused children that run away from home. It's from the view of an utterly depressed child who has got caught up in something he can't turn back from. The firefly without a light means he has no direction, and the blowtorch burning refers to something or someone that is so bright he is dramatically drawn to it ("it" being running away). I think the line "can you help me remember how to smile" refers to his idea of an alternative life away from his abusive home rather than a particular person. So he reaches a point where he finally cracks and runs away thinking that even living on the street will be better (easier than dealing with the pain), but finds out that it is just as bad as it was before.