I told her that I felt lonely when I was with my classmates, and how I thought only my teachers liked me.

我告诉她，当我和同学在一起时，我感到孤独，认为只有我的老师喜欢我。

youdao

Because I am lonely only when you cannot see me.

因为我只有在你看不见我的时候，我才最寂寞。

youdao

I'm lonely only when I am overtired, when I have worked too long without a break, when from the time being I feel empty and need filling up.

只有在我过度劳累的时候，在我长时间不断工作的时侯，在我感到内心空虚，需要充实的时候，我才会感到寂寞。

youdao