故人已去旧梦已醒
[gù rén yĭ qù jiù mèng yĭ xĭng]
Means that 'old friends/acquaintances have gone, old dreams have faded'. Used to express that one's once cherished friendships and aspirations are now things of the past. It's often employed to express regret over vanished days or a state where you've outgrown those memories.