3 sentences

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

3. 老师的一番知心话，让沮丧的他重新振作了起来。

   lǎo​shī de yī fān zhī​xīn huà, ràng jǔ​sàng de tā chóng​xīn zhèn​zuò le qi​lai.

   The teacher's heart-to-heart talk cheered him up from his depression.

   Source: Dong Chinese Dictionary