fairweather
adjectiveUK /ˌfeəˈweðə/
US /ˌferˈweðər/
A fairweather friend is someone who is only your friend when things are easy and fun.
He was a fairweather friend who disappeared as soon as I needed help.
OTHER MEANINGS
2. Used to describe good, calm weather with clear skies.
We set sail in fairweather conditions.
3. Describing someone who only supports a team or cause when it is winning or popular.
Fairweather fans left the stadium early once the team started losing.
4. Suitable only for calm and pleasant conditions.
The small boat is a fairweather craft, not meant for storms.