这部电影的剧情很悲哀。

Zhè bù diànyǐng de jùqíng hěn bēi'āi.

The plot of this movie is very sad.

这爱情小说也太悲哀了吧！

Zhè àiqíng xiǎoshuō yě tài bēi'āi le ba!

This romance novel is way too sad!

最悲哀的事是你爱的人不爱你。

Zuì bēi'āi de shì shì nǐ ài de rén bù ài nǐ.

The saddest thing is when the person you love doesn’t love you back.