Separated living in the same house..huh?

[Dom R]

As the story unfolds more, I found out she started seeing someone pretty much right after we Sep.

sounds more likely, "she found someone right BEFORE you separated".
hence the separation, and then the push to get you out of the house, so she can be with him more freely.

I think that you would probably do well in treating your situation as,

"Our marriage was lousy; my wife is now having an affair with an in-house separation; what do I do?"

If you read the relevant areas/posts/etc, with that frame of reference, I think you'll start looking at things differently.

There are lots of suggestions for that sort of thing. So I wont attempt to write much more on that right now, apart from saying,

"Her view is that she mentally divorced me 3 or so years ago." sounds like a hardened "walk away wife". so you have a gruelling, uphill battle in front of you.

She says I am content with where we are. I say I don't know how to get away from where we are and get back to what we once had. Is it even possible to get there again? Are we too different now?

you cant go back.
The question is, can you go forward, together, as the people you are today?
It's not a matter of "cant". it's a matter of willingness and interest by both people.