I hadn’t thought about it that way. I think, in general, turned vampires can evolve emotionally, just as humans can. It’s not like in typical vampire lore where, upon turning, the vampire loses their human soul or becomes a dead demon.
Granted, being immortal will have its own trials and tribulations, and different people would deal with it in different ways, which I think is shown well when A and N are contrasted. N longs for “human” things and having that contact because they miss being human, it seems. A, on the other hand, despises humans and anything to do with them, even though they risk their lives to keep them safe. A has grown more distant with time, whereas N has never lost that desire to feel connections.
F is much like N, except they don’t seem to understand certain things due to being raised in Echo World. F takes things in stride more so than any of them, but is also more aware of what’s going on around them.
M, on the other hand is very much like A–cold and standoffish, not giving a shit about anything human and not liking them much, either. A is more emotionally aware than M–this is one reason I get so damned mad at A, because they know they hurt the MC and are doing it on purpose to protect themselves from possible pain–but M’s hypersenses should allow them to pick up on things much the way F does. But M just really doesn’t care how anyone feels and sees no reason to behave any way other than hostile to most everyone because (apparently) being an asshole hasn’t kept them from getting sex from whomever they want.
I honestly see this as more of an M thing than a vampire thing, and not because of M’s memory wipe. It’s more of a choice or a habit than anything. M doesn’t want attachment, period, except for UB (not including the MC, because M wants no attachment to them at all). Sex is sex to them, it’s like scratching an itch and they have no desire for it to be more.
M has also never behaved as though it was more. In the last chapter of b2, when M is watching the MC before Rebecca shows up, they think that they only recently recognized they keep doing things with the MC they wouldn’t normally do. I really think that’s what the bakery scene was about–when M kisses the MC it’s totally different than usual, and that hits them, so they get pissed off and tell Haley the MC is nothing to them but sex (or wannabe sex). In that moment, it didn’t come off as confusion, it came off as a conscious decision to force the MC into the same box as the other billion people M has screwed–i.e., letting the MC know that they mean nothing, but mostly doing it for M’s own sake, to remind them of what they are (kinda like A’s tendency to immediately push away the MC when they get too close because it is shaking the foundations of A’s denial).
However, if what you’re saying is true, then there’s really no way for M to break that lock without getting their memories back. In that case, it’s not a choice but a physical/magical barrier that keeps them from having and acknowledging feelings for the MC.
And, really, if Sera intends to drag things out for M for another two books, then this is the only way it could make sense. It would also line up well with the misery of book 5–M getting their memories back may be a catalyst for other misery, or it may be one of the things the big bad of that book does to hurt the team and the MC. But that would mean M would be able to feel and acknowledge love for the MC.
I’ve believed all along it will be book 5 before we see M admit their feelings for the MC, and figured it will be book 6 before we see an actual relationship between M and the MC–if M’s ability to develop emotionally is dependent on getting their memories back, then at least it would be more believable (and more tolerable) than M just being an obtuse idiot for such a long time.