@pejejwrori At the risk of stating the obvious, this manga, Horimiya, and others like them are fiction. Fantasy. They are specifically created as a warm and inviting world to either induce a sense of nostalgia in people who had similar experiences or of wish fulfillment for those who simply didn't. You don't need to feel bad about your life because the immensely meaningful relationships and (somewhat) life long friends that are usually depicted in these kinds of stories are, truly, rarities in real life. At the very least, the most meaningful relationships of your life don't all come before you turn 25; they come and go in various points in your life, perhaps even near its end. Many to most relationships are as you described: casual and circumstantial. Media like these are popular BECAUSE many, many people want to escape this reality and the lack in their own lives.
A fictional person has no worth; you do.
(Sorry if this sounds like a rant, but after I saw your comment, I wanted to speak my mind.)