Not long after that he resigned.

那以后不久他就辞职了。

He dropped out of the race not long after.

不久之后他退出了比赛。

Not long after, a guard came in, waving a blindfold.

不久之后，一个看守进来，手里挥舞着蒙眼用的布条。

I handed in my letter of resignation not long after that.

之后不久我就递交了辞职信。

But not long after I said no, the regret started growing.

但是在我说NO不久我就开始后悔。