I'm so relieved. 我简直松了口气。

知识点：

I am relieved.

我松了一口气。

Knowing that I didn't get cancer, I was relieved.

知道自己没有得癌症，简直是松了口气啊。

I am relieved to do…很放心做...

He was relieved to see Jenny reach the other side of the street safely.

他看见Jenny安全的过了马路很放心。

That's a relief. 真让人松了口气。

A: I heard he made it to the top of the mountain safely.

我听说他安全的登上了山顶。

B: Oh, that's a relief.

真让人送口气。

I can breathe easy/easier 我可以呼吸的更轻松一点儿了

I can breathe easy now since the school is finished.

这个学期结束了，我可以放松了。

I can finally breathe/sleep. 我终于可以睡觉了。

Now that everything is finished, I can finally sleep/breathe.

现在所有事情都完成了，我终于可以睡觉了。