Another thing I keep thinking of is all the arguments we had over the years, or all the stuff we said to each other and never mean in silly little rows.
This is normal.
Everything you are feeling is normal.

As for the diagnosis, I'm not surprised you are angry.
But you were not to know. It wasn't your responsibility.
Whether something could have prevented the final outcome, no one knows. But it's not your fault in any way or form.