why does the word 'leave' mean“离开” and "留下" at the same time?
First situation, one person leave the house, I know the mean like this.It is meaning the person and the house will be separated.
Second situation, one person leaves, I don't sure if he is stay here or not.
Because in Chinese, 离开means somebody go away and not stay somewhere, 留下means stay and not go away. But the word 'leave' means both 离开 and 留下 at the same time.
I don't know if I have express the question clearly, sorry and thank you.

Question

why does the word 'leave' mean“离开” and "留下" at the same time?
First situation, one person leave the house, I know the mean like this.It is meaning the person and the house will be separated.
Second situation, one person leaves, I don't sure if he is stay here or not. 
Because in Chinese, 离开means somebody go away and not stay somewhere, 留下means stay and not go away. But the word 'leave' means both 离开 and 留下 at the same time.
I don't know if I have express the question clearly, sorry and thank you.

Answer

I think you are confusing two different words "leave" and "live". They might sound similar but they are not the same.

leave = go away and not stay somewhere
live = stay and not go away

Answer

I think you're reading too much into it.
If you left. you went away from the place just mentioned.
if you leave a place, you go away from a place.
If you leave something in a place, you still go away and that thing stays.

Answer

leave表示留下的时候要加宾语，而且其实是一样的，比如I leave him alone就是我离开了他，也可以理解为我留下他一个人，或者最常见的I leave the pen,我落下了这支笔，其实从某种程度上也是我离开了这支笔。单纯的sb leaves指离开