Amazing job! This is one of 3 or 4 rewrites (that I've seen) of that scene from episode 5, and is so far the best.

Absolutely gorgeous. Mikasa's emotions were spot on.
THE FEELS

It is a very good fic really :D

Great.

The thought process doesn't sound much at all like Mikasa frankly. You have to remember, she's not just the quiet sort, she's both dependent on and protective of him. Language referring to him as 'stupid', a 'bastard', etc is completely against her nature. Even when she'd temporarily given up hope without him she was mostly numb with pain, and then resolved to continue living because he taught her to and also if she were dead she wouldn't be able to remember him.

Normal people might go through brief stages of anger directed at their lost loved one, but Mikasa seems utterly incapable of it.
Some of the other lines seem a shade too informal too, but that could be entirely a matter of personal interpretation.