be somebody's affairPRIVATE/PERSONALif something is your affair, it only concerns you and you do not want anyone else to get involved in it 是某人自己的事 What I do in my free time is my affair. 我在空余时间做什么是我自己的事。
be somebody’s affair• What I do in my free time is my affair and nobody else's.
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