Its Just My Baby Daddy or Is it? Paternity Nightmares?

Women who tell men this is your child until the paternity test proves wrong? What is a man to do? Should he continue raising the child as his own or is it okay for him to bail out? A man pays child support for years and years just to find out the child is not his? Should the mother of the child repay him for all the years he paid child support for a child that was never his?