I shouldn’t have done that.

我真不应该那样做。

It was too late now for repentance.

现在后悔已来不及。

I’m sorry to have missed the chance.

我很后悔错过了那次机会。

I regret that I was angry with my roommate.

我后悔不该对室友发火。

I have regrets about not telling my friend the truth.

我后悔没有告诉朋友实话。

I feel so regretful; I have damaged your favorite bag.

我真是很后悔，把你最喜欢的包给弄坏了。

I really wish I hadn’t done it.

我很希望没那么做。

He is repentant of his sins.

他对于自己所犯的罪后悔不已。