Smells like they both have certain "issues" at their respective homes, so that this strangely-decorated house is their mutual sanctuary when things outside get rough.
And if I didn't know better, the guy is the one acting all 'tsundere', rather than the girl.
Ah, Tsundere Vanilla goodness.
Hmm...So did she build that place just for the two of them? They seem to spend time together there, and she does mention it was made with love...