私事

zhè shì tā de sī shì yǔ nǐ wú guān

这是他的私事，与你无关。

This is a private matter for him, and it has nothing to do with you.

bù gāi yóu wǒ lái shuō sān dào sì zhè shì nǐ men liǎng gè rén zhī jiān de sī shì

不该由我来说三道四，这是你们两个人之间的私事。

It's not for me to pass judgement, and it's a personal matter between the two of you.