If his wife were a "real woman" she wouldn't have had sex with a man (or men) not her husband. Were his wife a "real woman" she would have come clean after the infidelity took place and accepted whatever choice he came to concerning their marriage. Were his wife a "real woman" she wouldn't have taken the secret that six of his seven children are bastards to her grave.
Ultimately, a man should not be forced into caring for children who are not his own unless he has taken legal custody of the children. What a man's affections might be for a child and what a child's affections might be for a man should have no legal bearing as to who holds primary responsibility for the child and legal, primary responsibility should rest with the two people who created the child. Claiming that a man deserves to bound into financial servitude for two decades to another person in the "best interests of the child" is not much different than the argument Leftists make that the rich need to be soaked in the "best interests of the poor."
What if the biological father is never found? Then the biological father is simply never found and the child grows up without. Welcome to the club we have plenty of room in the member roster. What if the step/sort-of-kind-of/foolin'-around-with-your-mom daddy decides to give the kid some stuff, then cuts the kid off cold along with the mom? Well, then the guy is kind of a douche, but there is no law against being a douche, nor should there be. If a man who is not biologically decides to be a father-figure to a child, then that should be his decision, reliant upon his own conscience, not what the state decides (because as we all know, the state does no wrong) is in "the best interest of the child."
No doubt, but her conduct and behavior doesn't have anything to do with his personal relationship with any amount of children he recognized as his his own.
One common pattern on this thread is a fixation with the misconduct of the mother, though it is peripheral to how an adult male should carry his continuing relationship with children who recognize him as dad. That relationship is valid no matter how poorly the man's wife behaved - it really doesn't have much to do with the relationship at all.