Naruto... Does Gaaras monster break free from him?

No it doesn't. It is like a parasite. It can't leave Gaara's body, when Gaara does the Art of the Sleeping Possom he simply goes to sleep and lets the monster take control of him. He is still attached to the monster and the monster is still a part of him. He, like Naruto, can't survive without their monsters inside of them. So it is kind of like a life long disease. This doesn't mean that they are bad characters though.