@UnknownSaint111: Normally, I'd say you have a point, but they are trying to keep their relationship a secret. Whenever they do the deed, I think the chances are good that their physical interactions with each other will become more intimate (not lewd, just charged with romance); Mone-san, intelligent as she is, is nonetheless a passionate lover and already lets a good number of things slip (such that the secret should be out already), and already has a hard enough time keeping her hands off Haruta when alone, at times (this is part of her appeal).
It's all one of Mone-san's good ideas™, anyway.