Ethans reactions to Mia the whole game are kinda off anyways. He finds his wife alive after being presumed dead for 3 years in the beginning of the game and he's just like "what are you doing here?"
I get the game didn't want to get too emotional or serious but Ethan and Mia's relationship feels off.
This is basically Ethan's reactions to Mia throughout most of the game.
Wife is missing for 3 years. Finally finds her, doesn't act concerned of her well being and immediately asks what happened.
Wife turns into a terrifying possessed killer with a knife, and later starts banging her head against the wall so hard she collapses. Acts unfazed, doesn't find a way to secure her like bind her and even attempts to leave without Mia.
Watches a tape of Mia getting chased and eventually caught by a deranged woman with a complete lack of personal hygiene, especially between the legs. Doesn't sound concerned in the least bit and just says "What the fuck did they do to you, Mia?"
When Ethan reaches the old house, he finds Mia again, only for her to be dragged away by an even more mentally unstable man who was almost giving off rape vibes. Doesn't attempt to find a way around the fence and just goes "Nope, serum is more important no matter what that asshole does to Mia!"
Mia saves him from the mold in the ship and pushes him out the door, locking herself in, giving the impression of self sacrifice. Suddenly, Ethan really cares about his wife and almost feels unwilling to move on. Or on the other hand, forced to kill Mia and suddenly greatly mourns her death as she fades into oblivion.
Finally, both made it to the chopper and Ethan is glad that Mia made it. He even has rejuvenated hope and is in high spirits that he and Mia are going to start over and fix their relationship, so much so that in this ending, he sees this as the possible next door after this one closes.
Inversely, if Mia dies on the ship, Ethan watches the video she sent one last time and throws his phone out. He is basically devastated, the only door he sees is closed, metaphorically meaning he has lost all hope in his life and has no other reason to go on.
It's pretty weird, indeed. Ethan almost switches from "I married her because of corporate reasons" to "I genuinely love Mia and can't live without her". I wonder if this was intentional, or due to poor writing of their relationship.