If "~(으)ㄹ걸 그랬다" ; "~지 말걸 그랬다" and "~았/었어야 했는데" are used to express regret of something...
How can I differentiate them?
When is better one upon the others?
In which context is better one than the others?

I hope you could help me.
Thanks in advance

Question

If "~(으)ㄹ걸 그랬다" ; "~지 말걸 그랬다" and "~았/었어야 했는데" are used to express regret of something...
How can I differentiate them?
When is better one upon the others?
In which context is better one than the others?

I hope you could help me.
Thanks in advance

Answer

~하지 말 걸 그랬다 or ~하지 말았어야 했는데 is can be transferred to "I Should not do that in the past"

~할 걸 그랬다 or ~았어야 했는데 is "It would be better if I do that in the past"

Yes they are regretting, however, one is you did something, other is didn't do in the past.

Answer

Ah, I misread the two first as one. Then the second is the negation of the first. And the THIRD is the same as the SECOND in my previous comment.

Answer

And the third?

Answer

I'm not entirely sure, but I think the first one is about regret for something you didn't do, second  (edit) for something you did do and the third (edit) one is about something you had to do (whether or not you did it). But I may be wrong.