In the first question it would mean that the old friends either left their jobs or distanced themselves from the one who got promotion probably due to jealousy. In the second question it would mean that all his friends eventually disappeared from his life after the divorce.

Like Ernest, I have never heard that expression "fall away" used like that. The expression I'd use is "to grow apart", which means exactly what your examples intend: to gradually move to a less close relationship with someone (friend, partner, etc) A similar one, more radical is to "fall apart". This has a meaning closer to "disintegrate", can be used to refer to things, or to relationships. But it conveys a much more drastic/dramatic change in circumstances than "grow apart", which is gradual.

Laura, thanks for your explanation.

It's a colloquial phrase but I don't think it's something we would use commonly. It means that they stopped being friends, but without any event (like an argument). So... They started spending less and less time together, calling less often, until they weren't really friends any more.

Ernest, I see. Your example conveys a meaning of something like "to disappear", right? But in my examples, the meaning conveyed is something like "to stop supporting."