I don't think Takuya-kun's so much dense as just uninterested and happy to be a friend as long as Nakashima-san doesn't push her (assumed) pursuit of him. Okay, he's still dense too, but not like it's going to be the main running joke that just annoys you? In a more natural way?
The mom is drawing some parallels with her ex-husband (even the unintentional one of Nakashima-san's bad cooking). And from the blush and the way the story has gone so far and the early concept art, I get the feeling she's gonna be the type to get flustered and panic but not actually try too hard to fight her off cause she's kinda interested. It's going to be awesome.
Also, Takuya-kun's friends just being dumbfounded by his apparently sister-like relationship with Nakashima-san should be a recurring thing.