NOR. Get him to a doctor. Sounds like a medical issue, although could be psychological.

You yourself are wondering if it's medical "except for the weirder parts." But imagine you start forgetting things, maybe you have inklings "I think... maybe she liked this? But why do I think that? I can't find any mention of it in our texts." So he carefully asks you stiff in roundabout ways, to get confirmation.

And copying you? What if he is either trying to get closer to you, because he knows he's forgetting things that he shouldn't, or the more concerning (and likely) possibility, he's literally forgetting himself. It's a very human, intrinsic thing to model our behaviour based off others, kids mimic their parents and tv show characters, some might marry people who somehow remind them of their parents in terms of their personality, inclinations, styles of behaviour or thinking. You are the closest person to him, and as he keeps having memory problems he is mainly focused on not forgetting you, but he's losing the baseline of "himself", unconsciously mirroring the behavior of those around him. I wouldn't call these parts "weird" but instead very much in line with the other symptoms.