Can he press kidnapping charges against me for our unborn child if I leave the state?

No. Love, faded or otherwise, is not proof of paternity. He could initiate a paternity action, although doing so before birth isn't likely to go very far. Do understand that even though love may fade, even dissolve, if you and he have created a life to come into the world, you both have legal and moral responsibilities to do right by the child, from now to adulthood, and beyond.