2 sentences for 知心 (zhī​xīn — intimate)

1. 他们俩志趣相投，很快就成了知心朋友。

   tā​men liǎ zhì​qù xiāng​tóu, hěn kuài jiù chéng le zhī​xīn péng​you.

   They share similar interests and quickly became close friends.

   Source: Dong Chinese Dictionary

2. 在这个世界上，很难找到一个真正的知心朋友。

   zài zhè​gè shì​jiè shàng, hěn nán zhǎo​dào yī gè zhēn​zhèng de zhī​xīn péng​you.

   It is hard to find a true intimate friend in this world.

   Source: Dong Chinese Dictionary