What does "for good" mean here?
Native speaker’s answer
Rebecca
Yes, you are partially correct. "For good" is an informal way of saying permanently, forever, or definitively. It does not necessarily mean that something has changed for the good. In the song, the singers are saying that they have changed permanently. Ex. The couple ended their relationship. They were done for good. Ex. The treatment was successful! Her father's cancer was gone for good.