Yup, we're probably in for some stupid misunderstandings that could've been resolved with just some simple communication. Though, you've gotta realize she's never been honest about herself before, but she's very obvious in her body language, and the dude does realize that.
I do find the big brother annoying as fuck too, tho. And I bet she's stupidly naive and hasn't been listening to the warnings at all. Classic shoujo, gotta bear with it.