What's Hamlet to you, or you to Hamlet,
That you should weep for him?

What is Hamlet to me when he is grieving the death of cherised kin?

Devestated, confused, disconnected from reality. A part of the brain shuts down, as if lost somewhere with that love. No one knows exactly what takes over, but change will occur with every Great Loss. With time perhaps a piece of what is missing can be regained, there are no guarantees. How well one copes is dependant on surrounding circumstances, condition of the mind, and the strength of their soul. Death is a fight for survival, a fight against more than just the demised.
Hamlet is in much more of a hair ripping, ming racing, soul shredding situation than I have ever experienced. If I wept with grief for me before, I should weep for him.

What am I to Hamlet when I have been betrayed?
I am the people he fights for in the army, his fellow countryman. He will defend the honour of me amongst other patriots, and the noble country.
A companion in having a traitorous family, whether the family member intended to betray or not.
Nothing but a foolish green girl, a simpleton who should not disturb his turmoiled mind with her petty problems.
Or perhaps the only ear that will listen, relate, and empathize.

What is Hamlet to me when he is attempting to keep a handle on reality?
He is I, every moment, every day. And neither of us can tell if we are succeeding.