I've often written about my thoughts on friendship, and what I would consider to be its demise in American society in general. That generality is that I don't personally believe that what most Americans consider friendship to be is actually a friendship, but rather just a favored acquaintanceship. Others from elsewhere in the world will have to comment on whether or not this is the case often times in other societies. I also won't delve too deeply into the defining all the differences, but in general (and please note that I'm speaking in general), friendship trust in ways that acquaintances do not, and friendships require maintenance and time spent that acquaintances do not.
Another defining difference between genuine friendships and acquaintances is whether or not, and to what degree, that relationship can handle conflict and frustration. Everyone has arguments and most people have had instances where they have seen a relationship of whatever sort damaged or dissolved over an argument or some underlying frustration. A strong relationship, such as a marriage, often endures many arguments over time and stays together to work things out, assuming there was no irreconcilable offense such as adultery or something of that nature. And a friendship should be similar in the respect of working things out, aside from a grievous offense that no relationship would be healthy to remain with.
If your friendship when confronted with a frustration becomes an issue of one person having a problem and the other being both blameless and uncompromising, then you likely don't really have a friendship with them. Especially if your friendship doesn't survive an argument about common things that just need a bit of understanding and honesty...then likely you have mistaken an acquaintance for being your friend.
Again, there is nothing wrong with having acquaintances, favoring some of them over others, or facing the realities of frustrations with relationships we have. My primary point is to make it clear that there is the possibility of close relationships that are not spouses or 'significant-others', and that acquaintances shouldn't be mistaken for those close relationships. No offense meant to any acquaintance that I or anyone else may have, as in this life we need you too, but the differences between what an acquaintance is versus what a friend are so often not understood, thus precluding in most cases the notion of what genuine friendship even is, and usually removing that from the table of what relationships a person can have.
My hope is that we wouldn't sell ourselves short with relationships in the short time we have on this dirt-ball in space.