sit down with someone 和某人讨论

没错，sit down with someone不是“和某人坐一起”，而是“和某人讨论”。

例句：

I'll sit down with her and decide what to do next.

我要和她讨论一下，决定下一步该怎么做。

I will sit down with John tomorrow and see if he will change his mind.

我明天会和约翰谈谈，看看他是否会改变主意。