I think this song is about a guy madly inlove with a girl.
But the guy took the girl for granted at first and when the girl left, the guy realized how he truly loves her and was saying, "I can do better." It means he wanted a second chance with the girl.
And the guy is saying in, "Don't tell me I can make it on my own," the guy can't go on with out the girl even though the girl said he can.