Adaptation First: It's based (very loosely) on the short story "Memento Mori" by the director's brother but that story wasn't published until after the film opened. It's included on the DVD.
The short story actually has a lot in common with The Dark Knight, as many of Earl/Leonard's inner monologues are The Joker's verbatim.
So the question is not "to be or not to be," because you aren't. The question is whether you want to do something about it. Whether revenge matters to you. It does to most people. For a few weeks, they plot, they scheme, they take measures to get even.
You probably were the type to let it go, weren't you? Before. But you're not the man you used to be. Not even half.
Never-ending grief, never-ending anger. Useless without direction.