"
Because of you, I'm gone for good and that's the truth.
Because of you, I'm gone for good, I'll be brand new.
You can break me down, just like you did before.
Because of you, I'm gone for good and that's me over and out
So he's basically saying "F**k you I don't need you in my life, I can be a better person without you!"
But in serious terms he is saying that this person treated them like utter sh*t, and he's finally taken a stand and left said mean person. That makes him the better person, and he's happy with that.