i wanna talk about these lines
honestly when i first read them, they seemed a little weak (?) to me? It's pretty clear Arita already knows that (in principal) their relationship will be fine even without the right explanation. But the fact of the matter is he can't bring himself to really believe it. It is because he can't accept that idea that he's resigned himself to looking for a way to gain understanding (and explanation) anyway.
So for Takeda to conclude with "but you know arita even if you can't find the right words for it, what we have won't disappear" feels like he's just reiterating the previous point of "but Arita, it's fine if others don't understand", effectively ignoring Arita's issue. For Arita, that ship has sailed. He has already decided the idea that "they don't need others to understand" is just not enough for him. Hence, why he has moved on to his hunt for an Explanation.
In fact, just before his conclusion, Takeda even as good as justifies Arita's worries with a whole spiel about all the hardships they would face without a definite answer.
To end it with "buuut nah actually it's ok even if we don't have the words" sounds like a flimsy dismissal of those hardships.
But weirdly enough, although initially Takeda's conclusion sounded logically trite to me, i still felt the emotional significance of his words. And i realise that's probably because what Takeda is emphasizing here isn't "even if you don't have the right words", but rather the latter half:
"...what we have won't disappear."
Arita's breakdown comes as a result of him wanting the understanding of others but not having the words to make their relationship understood. But what about that understanding is really so desirable to him?
Imo the core of Arita's motivations in this arc can really be seen in the phone call with his mum in ch30. Because although prior to ch30, Arita has been troubled by the lack of words to explain their relationship, he had mostly just brushed it aside before.
But here suddenly Arita is faced head-on with the fact that having their relationship be seen as "temporary" naturally means everyone expects that it will end (which is obviously something arita does not want). If everyone around you was expecting your relationship to end, you'd naturally feel anxious and insecure, wouldn't you? Or maybe even pressured to end it at some point since that's what is "supposed" to happen. Even though Arita and Takeda themselves are quite secure in their relationship, the expectations of others makes Arita doubt it.
So Arita decides that he at least needs something, anything to make others understand that their relationship isn't just like that.
If "roommates" are eventually supposed to split up, then well they just need to prove they aren't "just roommates"! By finding an Explanation, Arita hopes to remove their relationship from that societally-predetermined box (and its implied expiration date), so he can get that affirmation that no, it's not a given their relationship will/has to end, and that what they have isn't doomed to fail.
But eventually Arita is left at a dead end. He can't find the words to explain their unconventional relationship, and his attempt to redefine it as something more conventional (and thus, understandable) didn't work either. At the end of ch32.1 Arita is left troubled because if it's impossible for others to understand, it's impossible for him to get that affirmation and sense of security he needs (or so he thinks).
But that's where Takeda comes in! Takeda (observant as always) is able to identify the real root of arita's distress (the fear of their relationship's instability). And although Takeda can't grant themselves the understanding of others', he rightfully recognises that that was not important to begin with, but rather just a means to the actual thing Arita needs: reassurance! So those final lines of his are technically ignoring Arita's current "problem" of not being able to be understood because they instead are cutting right to the heart of what Arita's really worried about: the security of their relationship.
Even if you can't find the right words for it, what we have won't disappear.
I must've misread these lines upon my first read because I read them like a counter-argument to convince arita that the words don't matter, when in reality they were more like a promise.
Because Arita doesn't need someone to tell him that understanding won't dictate if their relationship disappears. He already knows that fact in theory. He just needs Takeda to say it. Because then it's no longer just a fact, but instead a Promise. A promise that no matter what other people think, they won't let it disappear.
But I'm pretty sure Arita (like me) didn't immediately understand that promise for what it was, which is what led to his initial underwhelmed reaction to Takeda's words. He says he should've expected that answer, because he also understood those words as a simple repeat of Takeda's "it's ok if others don't understand" philosophy.
Arita does get it in the end (though the time it takes for him to understand probably causes his delay in reaction). When he finally understands the significance of Takeda's promise, that's what ultimately moves him to tears, as he gets the verbal confirmation from Takeda that they're not letting go of each other any time soon. The whole time, Arita thought the reassurance he needed could only come from society, but it turns out it could come from Takeda too.