let someone down

finally, i need to prepare for the olympic math contest next year. i can't let someone down who always care me.

最后，我要为明年的奥林匹克数学竞赛准备。我不能让关心我的人失望。

you let your guard down, you start to really care about someone, and I just-

当你卸下心防，开始在意一个人的时候，我无语了……

To slow down, you can just let go of the gas without doing anything else if you are just slowing because someone cut you off.

关于减速，如果减速只是因为有人干扰您，您可以停止加油，而不做其它动作。

When the drama ended, someone especially assigned for the task let down the curtain.

这场话剧演出一结束, 就有专人放下了帲幪.

Find someone who will let you talk things through, or failing that, write down your thoughts.

找个能让你把事情说清楚的人，如果不行的话，就把你所想的写下来。