Well I doubt he was thinking of confronting Rin for Yuu's sake. He did say it was her private life, and even while he was prying into it he knew it wasn't any of his business.
Yeah, but he was totally lying to himself there. He really wants it to be his business. And Yuunagi's dad frankly expects him to be nosy. He's just a chicken (which oddly enough probably makes him a better person than otherwise).
... but "you need to sleep somewhere, so have this house, and while you're at it, look out for Yuu".
The situation is just confusing. I don't think they are relatives, but they've known each other since they are little. So that must essentially mean their families live/d close to each other, 'cause how else would they know each other?
Now, I always thought that Yuunagi's parents did the usual manga stuff by going overseas, so Yuunagi is still living at home, just with her parents gone. But it might actually be that she moved out from home? And then Touka kinda followed after her.
But only until next door's where he's completely useless. So that's kinda my point - what's the point of this pointless arrangement? It's not like Touka was a homeless orphan, I'd assume. He didn't actually need his own house. ^^;