Pretty obvious. He can tell she is thinking of leaving him but he doesn't want her to. They are 'one of a kind'. He isn't going to force her to stay, but he will do his hardest to make her see. "I would do anything just to keep you with me." He warns her that she will regret leaving him "Don't you make that mistake" or perhaps he just wants her to feel that way.
Pretty obvious. He can tell she is thinking of leaving him but he doesn't want her to. They are 'one of a kind'. He isn't going to force her to stay, but he will do his hardest to make her see. "I would do anything just to keep you with me." He warns her that she will regret leaving him "Don't you make that mistake" or perhaps he just wants her to feel that way.