I don't think NeitheYAGI is planning this one out as much as his others. For one thing, that statement from him despite the clear attempts to sleep with him in other chapters, as well as her asking him if it were possible for them to be more than "friends" (chapter 14).
The other clue he didn't plan it as much: in chapter 18, she is clearly panicking over his safety after seeing Miharu deliver food ("We don't mess with the spiders!"). This is despite the past few chapters showing that she liked Miharu's brother in the past, and feeling safe enough to go drinking with her.
I like this story, but it could have benefited from better planning or acknowledgement of prior behavior.