Option 1 -> "Fair-deal" is not an established idiom to describe friends; it typically refers to transactions or agreements.
Option 2 -> "Fair-weather friends" is a common idiom meaning friends who are only present during good times but disappear during difficulties.
Option 3 -> "Far cry" means something very different from something else; not used to describe types of friends.
Option 4 -> "See through" means to detect deception or complete something; not used as an adjective for friends.
Hence, Option 2: fair-weather -> The sentence contrasts a genuine friend (loyal in all circumstances) with fair-weather friends (only present during favorable conditions), making this the perfect idiomatic choice -> correct