to begin a romantic or sexual relationship with someone

All my friends seem to be pairing off and getting married. 我所有的朋友好像都已成双入对，正在准备婚事。

Ravens nest very early in the spring and they pair off in the late autumn. 渡鸦早春筑巢，晚秋交配。

to introduce two people to each other so that they will start a romantic relationship

I managed to pair my best friend Sue off with Mike. 我设法让我最好的朋友苏和麦克成了一对。

If a group of people pair off, they divide into pairs in order to do something, and if you pair them off, you divide them into pairs.

The students paired off to practise their conversational skills. 学生们两人一组进行会话技巧练习。