Fair-weather friend

My Fair-weather Friends of the Summer are going away for London, and I ſhall ſee them and the butterflies together, if I live till next Year; which I would not deſire to do, if it were only for their ſakes.

[T]he liberty of the press was not to be looked upon as fit only for seasons of calmness, as a fair-weather friend to be discarded in a storm.

Ere long a portion of the village spire began to appear among the trees, and the gilded telltale on its top, in which the slippery politician, and the fair weather friend, and the doubting disciple, who is blown about by every wind of doctrine, may behold a happy emblem of life and practice.

She did not even attempt to make a reply, or to ask her fairweather friend to remain; but suffered her to leave the room and the house without a word.

Be not pestered with too many friends. […] There are as many grades of friends as there are plaids in the tartan. There is the friend of "ifs, buts, and ands," who always signifies that he would if he could, but as he can't, how can he? Then comes your fair weather''' friend, who deserts you the very first time you founder in the mud!

She put little nosegays from her garden on his desk, and tried in every way to show that she was not a fair-weather friend, but faithful through evil as well as good repute.

[Sandro] Pertini is being embraced as the leader of a staunch and increasingly important ally—a country that, as [Ronald] Reagan put it, "is no fair-weather friend but instead is an indispensable partner."

One respondent to a Gibbs and Humphries's research initiative characterised their senior management as ‘fair weather friends’ – keen to support the partnering initiative on day one and when things are going well, but eager to distance themselves when times got tough.