well this guy might be forced to depending on what State he lives in. In Canada and many US States once you 'assume' the role of the parent you are one just as if the kid was yours.
One of my best friends younger brothers who is a very successful dentist found out his kids were not his. His wife left him (before he could leave her) and she blamed him for being a workaholic as to why she strayed. She moved in with the father of her kids who did not work and she sued him for support securing big monthly payments from his successful dental practice. She bought a house with his money for herself and her new unemployed man and their kids with his money. 8 years later he is still paying and hardly gets to see the kids as she makes it difficult.
He has literally been forced to support not just her but the man she cheated with and the kids that are not his so none of them have to work regularly. And all because she committed a fraud against him that society won't call a fraud.