Sanami-san clearly has a cruch on Takayanagi, but it would never work out, Naganori is clearly a father figure for Takayanagi, if not The father figure, so on his eyes Sanami is probably just a lil sister
In essence in this chapter Takayanagi has to grief and deal with the idea of losing the dad he finally found late in life
why do people marry when they barely give a shit about each other ?
At least for Takayanagi it seems it was cheer social pressure, remaining single would have put him in awkward position at work, usually those kind of expectations are more heavily imposed on women, who are pushed to get married and have children before they hit 30, but it is not like we men are not immune to the same pressure even if it is way lesser
So I guess the girl we saw at the start of chapter 48 was Takayanagi'ex wife, Kikukawa. Maybe an old classmate, given that sensei knows her?
By the way, at page 12, is sensei really saying: "It figures. That's just how you are." Shouldn't he rather be saying "That's just how she is"? Or maybe, he's saying that because of the "might have" Takayanagi said before.
I think it still works as it appears in the chapter
Keep in mind that Naganori sensei is saying "It figures. That's just how you are" in response to Takayanagi saying that his ex "Might have cheated on him"
Naganori then makes emphasis on "might have, huh?", meaning that Takayanagi doesn't knows IF his ex actually cheated on him, nor made any effort or even bothered on finding out what really was happening with his ex, the relationship ended, and he still has no clear answers
Hence "It figures. That's just how you are", this is a loaded sentence, it exposes that Takayanagi is content with the explanation that from the start they were never a good match, and that it was normal for them to eventually breal up, rather than to focus on wether she was seeing someone else or not, as if it were something that is of no concern to him
While everyone else would have wanted to know more details, or find a transgression to blame the marriage ending on, Takayanagi would rather not delve into such things
That in itself also exposes that, Takayanagi was really detached on his marriage, his involvement and investment on the relationship was so shallow that he never really bothered to find out what his ex was doing, which in a way is also a form to avoid taking responsability for his own shortcomings, she may or may not have cheated on him, but he was clearly not involved enough, not even to the point of wanting to know if she was cheating on him
I always wanted to know more about Takayanagi's married life, but given this chapter i am now convinced that we may not get that side of his life, since it didn't appar to have been that impactful to him