fair-weather friend
nounUK /ˌfeə ˈweðə frend/
US /ˌfer ˈweðər frend/
A fair-weather friend is someone who is your friend only when things are easy and fun.
She stopped calling me when I was sick, so I guess she was just a fair-weather friend.
OTHER MEANINGS
2. A person who supports a team or cause only when it is winning or popular.
He only wears the jersey when the team is winning—total fair-weather friend.
3. A companion who disappears when you need help or money.
When I lost my job, my fair-weather friends vanished overnight.
4. Someone who stays close for the good times but leaves at the first sign of trouble.
A true friend stays through storms; a fair-weather friend runs at the first cloud.