I'm assuming marriage. There was the ring that shows up chapter one (I swear that's the only time I ever seen it, too.) Weird characterization choice, because it's straight up never talked about (husband also apparently married into the Takamine family, apparently. Also unusual). I always thought Hitomi was kind of the person Tsukasa needed behind him the way he doubts and self-deprecates himself. IDK.
Nah, Hitomi has always been Tsukasa's big sis figure. Chapter 37 really reinforces the fact that Tsukasa was basically the little brother figure of the club by how Kohei and Hitomi talked about him.