Thanks for the TL! The multi-page Abyss Rant (tm) and transition between her being with Mao and her being with Reiji are chilling. As for the rant itself, well...
I can see where people are coming for in terms of it not feeling very well paced-out or weirdly vitriolic but I'm kind of into it. Grief like Mao's isn't really a rational thing and it makes sense that he'd reach for the very first thing that gave him someone to blame for what happened, something actionable - not that it's at all an excuse. Nagi's not even old enough to menstruate, so of course she'd internalize everything he said to her, even if they're both hurting. She's a kid, so she's not going to be able to rationalize her way out of developing that baggage - even if he hadn't said anything, she probably would've blamed herself.
But what I really love here is finally getting context for what that smile she gave Shiba-sensei during the Tokyo arc actually meant. Good stuff.
Personally I'm leaning less towards grief and more towards manipulation because of what's about to come.
I suppose it could be both? It's hard to say, we don't know much about Mao's backstory and it's unlikely we will know much more. All we know is he's been through some fucked up stuff too.
I'm sure Ryo is aware that Mao's behaviors seem very extreme at first glance, maybe that's the intention? To force readers to think about why he's doing this, or to be in Nagi's perspective? Unfortunately for her, most people don't seem to be doing that.
I think she's gonna have to spell it out to everyone in the next chapter or 2.
Maybe (in that case you're right) when Mao abandons her after using her to get money, he tells Nagi why he said all of that and apologizes, but by that point it's far too late, and instead makes her feel more guilty and apologize for not understanding him?