Is expiation required again for doing something that was sworn to be abandoned, and then was done again after expiation for it?

Your oath was broken by the first transgression. You are not required to repeat the expiation unless you intended repetition when you made the oath. So, whoever swears not to do something and then does it, breaks his oath once, and no expiation is due for him thereafter unless he intended the repetition of the transgression every time he did it.