相思病是一种怪病
[xiāng sī bìng shì yī zhŏng guài bìng]
Love sickness is a strange illness — 'being struck with longing for someone can feel like a bizarre, uncontrollable affliction', expressing the intensity and somewhat illogical side of emotions tied to deep love or longing. This can relate not only to romance but strong affection or nostalgia for something long lost or unattainable.