That said, I think that on some level true friendship doesn't really exist the way the popular culture implies that it does, as a sort of adoptive sibling hood. Maybe that happens in a few cases but it's rare. What friendship really is, is a sort of "alliance", which explains
@WhitePolarBear 's reference to male friends being looks-matched, a true alliance is usually an alliance of equals, where it's more likely that both sides benefit. A lopsided alliance is not necessarily abusive, but the odds are increased.
I've seen a lot of cases by now (I'm 34) of friendships not lasting.
Sometimes that's because people lose touch due to growing apart, that's fine I don't have any objection to that. If that's happening, don't force a friendship as that will just alienate people. Let people go, if you happen to see them one day five years later you'll still be friends, as you won't have poisoned the well by trying to force things.
Other times it's because people prove themselves duplicitous. A friend of mine recently got into a disciplinary hearing at his position. He was in trouble, and wanted to get some character witnesses to speak on his behalf at his hearing, to say that he was a good man. He went to someone that he knew, someone that he had helped a year prior, he had helped her resolve a dispute with her landlord in an amicable manner that saved her a lot of money. He asked her to be a character witness at his hearing, he figured that she owed him a favour, and she had seen a good side to him, his skills at conflict resolution. He was disappointed that she refused. She didn't want to get involved. He said that it gave him a new insight into the meaning of friendship.
Why not to use "fellow" word instead?
It's not a commonly used word in my circles. I guess I could use colleague, mate, or acquaintance.
But at the same time different (obviously)
