for anon <3
it is true that jm and jk were always close, and tae and jk were close at one point too. i remember that a lot of the bangtan members used to call tae "immature" in yearly profiles (back in his 4d days), and in recent years they began to say he has matured. uh, i hate to bring this up bc it feels intrusive but it's true i think that losing his grandmother in late 2016 changed smth about him. he became very serious from that moment on; something about him sobered up, in a sense. then his close friend passed away in late 2017. and even though i don't think him and jonghyun were close friends, that passing impacted all of kpop and i'm sure it affected him too. his grandfather passed mid-2018 as well. it's possible that this created a disconnect between him and the rest of maknaeline, because even though everyone experienced the effects of jonghyun's passing, no one in bts has experienced as much loss as taehyung. he lost someone close to him every year from 2016 to 2018.
like u r saying, jungkook said in soop that tae becoming reserved made it hard for them to connect the way they used to, because they were playful back then. but notably taehyung says none of those things. he only says that they were "partners in crime" back then, but he doesn't mention a disconnect in personality the way jungkook does. (i just rewatched it: https://youtu.be/Bsyg2puVOGw) we can see that jimin and taehyung actually seem much more amiable and playful, at the beginning of this clip. we also know that taekook is the pair that had become significantly distanced, and vmin were not distanced to that extent. it's only jungkook and taehyung that have this particular type of tension. then -- icb i didn't notice or didn't see this before -- taehyung openly admits that he feels like he isn't loved, that he goes on weverse to feel like he is receiving love, and at night in bed that feeling evaporates....and not being able to see the love from fans with his own eyes has exacerbated that. he literally tells us this.
this is a bit subjective, but the way he says "we were partners in crime" suggests to me that he missed it. it's a source of nostalgia for him. the way he says that, i don't think he thinks he's too mature for them. it's not that jimin and jungkook haven't matured too. i think he wants to be close with them. but his life experiences took a trajectory that changed the way he is drastically, and while he may have wanted to remain close with jimin and jungkook, jungkook found it difficult to connect with this new kimtae -- and while jimin wanted to hang out with taehyung as usual and doesn't seem to feel a disconnect w kimtae's changed personality, jungkook began to dominate his time. and kimtae, who was losing loved ones one by one, and was now losing his connections with his closest links in bangtan -- no wonder he felt like he wasn't loved, ykwim? his life turned upside-down. he got closer to his actor friends, because what else was he supposed to do? jm and jk were (are) closer than ever, and more often than not it was (and still is) just the two of them. he reached out to people (his actor friends) who would reciprocate his affection, make him feel less alone. (T_T i know most people don't want to believe bangtan have insecurities like the rest of us but they are human too....)
but ofc distancing from a difficult connection and choosing to strengthen other ones doesn't magically heal existing rifts. the clip didn't show it, and unfortunately i forgot who initiated the soop convo in the first place, but lovely leaf reminded me that kimtae got jimin to help him have that serious talk with jungkook, which means kimtae did in fact want to fix things. he didn't think he was too mature for them; he wanted to be close again. and he finally took the initiative in soop.
and then we can see the results of how trying to heal those rifts has made him happier in butter era. butter era vlives....the smile on his face....it was like his younger self. it was like he felt loved again. i think if we look closely, we can find quite a few idols going thru dpression eras and coming out of them like they were reborn, like they're reinvigorated, like they are their old selves again. it's a noticeable pattern, imo (see, for example, najaem and lele). and kimtae's arc fits right into it.
so overall/tldr; i don't think kimtae felt too mature for jm and jk necessarily, because he eventually took initiative in soop to have a serious talk with jungkook and reconnect. he himself catalyzed the mending of their relationship.