@Robinisback
To be fair, those elements that are "missing" from this story are what make it that much more compelling, the mental/emotional dependence displayed here isn't window-dressing.
Of course they're all gravitating around each other, they've latched onto each other as interactive supports. Note, that's not the same as an emotional support, interactive supports are anything that keep you from exiting, even if it's unhealthy.
The mental health issues aren't just there for the sake of a scene/plot point. It's not just another part of a character's day, and I feel that's very accurate to what these situations and mental issues look like in real life. It's all-encompassing, it's exhausting, and it's rarely a good experience.
As for Reiji's seeming lack of agency - just going with whatever he's told - well, he's a kid. A chronically depressed kid who is well past the "I want to die" phase and is now resigned to whichever path has the best chance of "getting out".
First it was Nagi with a mutual exit, then it was Sensei with a way out of the environment, then Chako with leaving the environment, and finally now his mother.
Remember, this is called "Boy's Abyss" for multiple reasons. It's not just about "The Boy's Abyss" but also "Those who get sucked into The Boy's Abyss". He is consumed by the "Abyss" but is also an "Abyss" consuming others.
God, this has to be one of the most depressing yet personally validating manga I've ever read. Not just the situations, but the consistent low notes, broken up by lower notes that then become the norm.