The Kind of Talk That Keeps People Together

This is a thought-continuation from a previous post but there are what I call "conversation-quotas" in friendships.

Ex) You have a friend you'll talk to for a semester because circumstances are favorable because of close proximity and mutual sessions of free time. Conversations within this semester are deep, easy-going, honest, enjoyable, and they develop the relationship further. However, after that class is over and you two have finished your final, despite the both of you still having free time and activities to talk about - the quality of such communication is noticeably less grand. Yet, sometimes there are people you just keeeeep on talking to, even if your schedules and respective locations change. If anything, the bond between two such people will gradually but continuously keep getting deeper.

Do you see how small talk exists like an indicator for friendship expiration?

(I've been transcribing too many interviews so now I'm picking up someone's manner of speech but) now I'm curious to know more about what exactly keeps two people close.

My thoughts aren't extremely well developed yet, but what I'm running with so far is that:
what matters to the core of one person is equally important to the other.

What that "core" consists of can vary over time, but if the "cores" are the same for the two individuals at any given point in time, then there will be unity and the necessary emulsifier to keep a relationship as smooth and lovely as dark chocolate ganache and not separate like water and oil @_@

In my personal experience, the moment people start drifting away from me in the relational sense is when what matters to me doesn't matter anymore to them (the likewise is the same as well). One person once told me "well i don't care about your feelings." Another time, someone was talking to me about something they thought I loved and I just keep nodding them off without responding at all  (which, to me, is as rude as anyone can be).

They can be things like anime or Christianity or feelings or music or clothes or ideals or philosophies. Whatever's central to one person needs to be central to the other. That centrality can consist of many parts, but I believe two people who can stay together share many of those parts.

I wonder if anyone's like that for me out there.