Answer:
I destroy your home from the inside out.
I am what bring things together. Without me everything you see would be a total mass or debris everywhere.
My first is in fish but no in snail. My second is in rabbit but not in tail. My third is in up but not in down. My fourth is in tiara but not in crown. My fifth is in tree you plainly see. My whole a food for you and me.
If you drop me I'm sure to crack but give me a smile and I'll always smile back. What am I?
What always ends everything?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.