Stories like this is one of the reasons why I don't respect cheaters.
Next, there is nothing funny about someone finding out the children he raised isn't his biological children. A man learning a child or children isn't his could really fukk a man up psychologically and emotionally, not to mention financially in some instances.
Lastly, I don't think it is healthy to develop trust issues when getting with someone, but people need to really vet the people they bring into their lives. Not everyone is solid. I will go as far as saying that it is rare to find a real one, especially during these times.
I agree with one of the posters who suggested mandatory DNA testing during births. If the mother is a real one, then she has nothing to worry about. If she isn't a real one, then the man has decisions to make which could affect his relationship with the mother.