I'm honestly surprised-
No, I'm not surprised. I can no longer say that.
We've got a textbook failed marriage here where the wife is starved for attention and is forced to do everything around the house as well as work(how do I know she's working? She's cheating with her manager). Of fucking course she's cheating on him, she can't be more obviously unhappy and the dude seems totally unaware of her obvious dissatisfaction. Should she divorce him? Yeah, obviously. But she also has his kid, and that's complicated to do, and shit man, I don't even know if Japan has no-fault divorce laws. "He sucks" may not count as a reason for divorce, and he'd have to file for infidelity. She says she wants the child to have a father and that's why she doesn't want a divorce, but she also hasn't realized yet that he doesn't in this marriage. She's been raising the kid all on her own, basically just living with someone providing child-support. Not a husband and father.
What's most interesting to me is a little bit of consistent characterization that shows a level of writing sophistication I didn't quite expect yet: she's got a habit of putting her foot in her mouth around unstable people. While she did literally nothing wrong in that interaction, honestly just trying to get her friend to see the upside of not having a kid yet, she accidentally stepped on the ONE landmine she shouldn't have: the idea that she's jealous of her. Because her friend is trying very very hard to have a child, but hasn't been able to. Since the sister isn't a gossip and honestly feels like she's too tight-lipped about her struggles for her own good, her friend has no idea that the reason she's always bringing her baby when they meet is because her husband is asleep and won't watch him. So to her friend, she's always parading around that SHE'S got a kid, and her friend can't help but feel like she's being made fun of.
This makes her feel like she's driving everyone who cares about her away. She's lonely already with her basically absent husband who sucks, but we've watched her accidentally step on the kid landmine twice and we have proof of her saying the thing she shouldn't have to her brother about his new wife, saying that a divorcee is too much trouble for him and that he should just go after a young girl at the office. A skillful bit of premature characterization there, too: a reader who remembers things will recall that when they see her own failed marriage. Why no divorce? Well, who'd want her after she divorced her husband?
Honestly, poor woman. I can only hope the manager isn't terrible, but I bet he is. What kind of asshole would fuckin' come inside a married woman having an affair, who was clearly turning to you because of emotional distress? Even if it got out of control and he ended up sleeping with her because of actual romantic tension and emotional intimacy, that's just ridiculous. It complicates everything.
I wish she was able to talk to her brother. She needs someone. He needs someone too, although I don't know who other than a reader would be able to figure out what the fuck he's trapped in. Even we don't actually know and after last chapter it seems like an occult ritual.