There are Real Friends and there are Placebo Friends. Real Friends are reliable and very rare. Everyone else is a Placebo Friend, part of the control group that stays with you only through the good times. That doesn’t make Placebo Friends evil. One can be both a Real Friend to someone and a Placebo Friend to another.

What are friends?
Friends are people that you think are your friends
But they really your enemies, with secret indentities
and disguises, to hide they true colors
So just when you think you close enough to be brothers
they wanna come back and cut your throat when you ain’t lookin’

Lyrics by Eminem, If I Had

Misfortune shows those who are not really friends.
Quotation from Aristotle, Eudemian Ethics