They are fair-weather friends.

他们是酒肉朋友。

youdao

Both countries have become all-weather friends that rely on each other.

中也两国已成为相互信赖的全天候朋友。

youdao

Im a bit disappointed in John and David. It turned out they were only fair-weather friends.

我对约翰和大卫有点失望，原来他们不过是靠不住的酒肉朋友。

youdao

The Saudis remain at best fair-weather friends to the US, while Israel's strength or weakness directly impacts US national security and geopolitical interests.

CENTERFORSECURITYPOLICY: America's best friends

But yes, some people who have been fair-weather friends, no doubt at those Krug and shepherd's pie parties, will steal away into the night.

BBC: Breakfast with Frost

What does seem predictable, however, is that at some point these arms will wind up in the hands of people who are not even our fair-weather friends.

CENTERFORSECURITYPOLICY: Saudi Friends and Foes