That’s not how this works, the new man didn’t help create the child.
The “genetic” parent is obligated for at least 18 years, no ifs, and or buts about it.
If you’re a single mother and you start dating another man, your BD is allowed to subtract funds when there’s another man in the picture. It don’t matter how rich or well off your BD is your new man has to help with some of your responsibilities.