just finished Chapter 22 so this is my reading so far.
Weeds grow in fallow fields, it's clear despite her issues she's willing and capable of improving. Missy clearly is socially retarded, which is entirely understandable, but so is Leo and he has no excuse. Leo is entirely forgetting the context that she isn't human while living in a human world, so her problems shouldn't' be surprising, yet he chastises her constantly with rhetoric that can only apply to a human, and arguable at that since I believe a person like Missy needs a very kind but firm hand and all Leo does is put her down and treat her like shit which only turned her into a beaten dog and not a self reliant one.
Now I don't know where the writer is going, but armchair experience to me implies Missy i suffering from abandonment issues, and possibly worse, fear of her own true feelings being an issue too, if the offhand comment about her leaving him when they were young is any indication. Coupled with her statements of trading sex for couches and other things like that(shallow treatment of intimacy), and her fear of losing him in the fog, and her obvious love of him, it's clear she is fearful to address that but she's codependent on Leo despite his emotional abuse.
Leo is obviously suffering from codependence as well, he hates his life, he's lonely, he hates his routines but can't get out of it, and Missy disrupted all of that. And all the complaints in the world about his old life doesn't change the fact that Missy is the best thing that happened to him, and he knows it, and it's clear he is falling in love as much as she is, but he's too much of a chickenshit to admit it to her and most of all himself.
There's also the aspect of their differing views on nostalgia, she's balls deep in it, she misses those days because they were happy and loves to relish in it while the opposite it true for Leo. However despite those different mentalities, they both see their childhoods the same, a time they believe was better than now, a time they wish they could experience again but never can. Missy loving the past and talking about it, while Leo angry that the future turned out so shit and he's resentful that he can't go back so remembering it is painful and not happy.
Also Leo just sucks, like whatever you think of Missy, Leo is a serious buzzkill in all ways, how the fuck do you go through life and never watch Godzilla? Fucking seriously? Or just shit on any fun at all, the guy is just awful.
also full disclosure, Missy reminds me of my fiance who is super fun and was broken at the start, so I'm projecting somewhat. Also I'm about 90% sure that Missy's species affects memory somehow, seems to be where that's headed.
tl;dr, this story has pulled me in way too fucking hard that I'm obsessively autism posting, so, GG to the writer