Fair-weather friend: someone who is your friend only when you are cheerful and successful.A lot of John's friends turned out to be fair-weather friends. They were with him when he was rich and left him when he went bankrupt
shoulder to cry on: someone who is always ready to listen to your problems.I'm so glad my friend is so kind and sympathetic, it's good to always have a shoulder to cry on.
to be through thick and thin: to have some good times and difficult times together.Your parents are married for 15 years, they must have been through thick and thin together.