There's a beautiful irony to Shion and Nozomi striving to act stable and relaxed around each other, making each think that the other has moved on from their issues, which causes both of them to grow gloomier as they bottle up their grief for fear of reopening a can of worms, which in turn causes the other person to grow even more worried because they can tell that the tension's building up, which further in turn causes them to either clam up even more to avoid escalation, until the point where they actually communicate and give each other more anxiety because now they're blaming themselves for not having noticed and said something earlier, but they can't actually say this because it would amount to making the issue about themselves, even as the other reprimands them for not sharing while being too afraid to be honest, and then... well, you get the idea. It's like two dominoes falling in opposite directions to avoid hurting each other and causing a collapse anyway.
Also, I was surprised that Shion went right for Heidi's gender, which initially seemed kinda rude, but considering that it's better than making arbitrary insensitive guesses, she might've actually gotten the right idea. I suppose it's the closest equivalent to asking for someone's pronouns in a nation that's rather different from the West, both in terms of language and societal attitudes.