Answer:
I am so delicate that even mentioning me breaks me. What am I?
Die without me, never thank me. Walk right through me, never feel me. Always watching, never speaking. Always lurking, never seen. What am I?
I can be thin but not fat; in your body but never on your placemat. I'm always better when I'm fresh but you'll never see me in the flesh.
I destroy your home from the inside out.
I have a brother. However much we run we do not reach each other.
The more of me you take, the more I appear behind you. What am I?