The phrase for good means that an action is final or permanent. We often use this phrase when talking about a change in our situation such as when we move to a different country. If you like your new country and you want to stay here permanently, you can say that you're staying for good.
A: How do you like New York?
B: I love it here. I want to stay here for good.
A: My friend Ronaldo hates it here. He can't wait to go back to Columbia.
B: Have you heard from Manuel lately?
A: Yes. He went back to Spain.
B: Did he return for good?
A: No, I think he'll be back in a couple of months. He just needed to take care of some things.
B: Really? That's cool. A friend of mine just left New York for good. He wanted to stay, but his visa expired and he couldn't get a new one.
A: That's too bad.
B: I know.
Alright folks, the next time a friend is getting ready to return to his or her country, you can use this phrase. You can ask, "Are you going back for good?"