We were separated by the crowd and I guess we left Stephan behind. Can you give him a call to see where he is?

我们被人群冲散了，可能把Stephan丢在了后面。你能给他打个电话问下他在哪里吗？

Leave sb./sth behind 超越某人，被某人落下

Study harder, or you're gonna be left behind by your classmates.

努力学习，不然就会被同学们落下了。

Leave sb./sth behind 把某物落下了

I left the bag behind at the restaurant. Let's go back for them before they get taken.

我把我的包忘在餐厅了。我们回去拿一下吧，以免别人拿走了。