Answer:
Long and thin red within with a nail at the end.
I belong to you but others use me more often than you do. What am I?
In my life I must bare my bloodline I must share.
Deep, deep, do they go. Spreading out as they go. Never needing any air. They are sometimes as fine as hair.
With pointed fangs I sit and wait; with piercing force I crunch out fate; grabbing victims, proclaiming might; physically joining with a single bite. What am I?
I never sleep yet sometimes I weep. I can get angry or just be happy. Wherever you go, I will follow. No matter what you do, I will be there. I cannot die. What am I?