How is Macbeth a nihilist?

It is important to note that Macbeth wasn't always a nihilist. At the beginning of the play he was a devoted husband and solider; it is only through his wife's death (as seen in his "To-morrow and To-morrow and To-morrow" soliloquy) that he thus embodies the true nature of a nihilist: "what does it matter?"