Fair-weather friend

[Sonia]

A friend who is only a friend when circumstances are pleasant or profitable. At the first sign of trouble, these capricious, disloyal friends will drop their relationship with you.

[Tina]

a psuedo friend. One who pretneds to be your friend when things are good. Leaves when things go astray or are not quite like they think they should be.

[Lanell]

someone who is a good friend when it is easy to be one and who stops being one when you are having problems