Last episode: Why did Kevin pretend he didn't know Nora and ...
when he first meets the "old" Nora/Sarah?
And why was she hiding from Kevin for decades?
Q1: He was desperately trying to start life over with her by trying to forget all their quarrels. He also wanted to make her genuinely believe he was telling the truth and thought it might be believeable given all the overnatural things that have happened both to them personally and in the world they're living in in general. Also, show creators wanted to take the audience for a ride.
Q2: She was massively depressed after everything that had happened to her. She couldn't take it any longer and wanted to leave everything behind. She wasn't just hiding from Kevin, but every one aside from Kevin's ex wife. These kinds of things have happened in real life too. She also most likely lied about what happened with that machine. Or maybe it had been so long she believed she was telling the truth. It is possible to do these kinds of mental gymnastics to yourself as a coping mechanism.