It slipped my mind.

我忘了。

I'm afraid I can't.

恐怕我不行。

Let's forgive and forget.

让我们摈弃前嫌。

Let's have fun tonight.

今晚让我们乐一乐。

He could always come up with a reason for them to linger another month.

他总能想出个理由来让他们再耽误上一个月。

He is hard to please.

他是难以取悦的。