I was recently watching Maury and I was wondering is there a mod that would allow for your spouse to think he is the father of anothers man child.

Could be mistaken, but I don't think there is any way to raise them to that level of awareness. Sims will take care of and raise any baby (toddler, child, teen) who appears in their household by any means whether they are blood related or not. They are only aware of cheating when it comes to the physical acts of romance themselves and rumors about them that their partners might be engaging in.

Kinky World might cover that, it has a much more complex cheating system, although I can't say I've ever paid any attention to that bit. Also adds the cuckold trait which will make a sim enjoy being cheated on (often combined with the voyeur trait), which sounds like it may appeal to you. As a warning though, the mod is mostly an overhaul of the woohoo system, primarily adding in animations.

I didn't know that about KW. But having that one in play is not conducive to long-running ongoing games and it is incompatible with many NRaas mods to the point of being game-breaking, in case that is of any concern.

The current version isn't incompatable with any of the Nrass mods that I'm aware of. Overwatch and ErrorTrap need some minor tuning and one the the optional packages respectively. Shooless becomes redundant can theoretically cause issues if you set it differently from KW (KW has settings for the same stuff, but I can confirm that KW overrides shooless if shooless is left untouched. Haven't actively tried to cause conflicts though). Woohooer can cause some permission conflicts and becomes a bit redundant, but as long as you keep your settings consistent between the two mods the only issue I've encountered is that you have two instances of each romance option for teens (if teen romance is allowed), which is a bit annoying but doesn't break anything.

Can't say I agree about long term issues, Ive had games on 5th or 6th gen with KW installed without any unexpected performance drops. Some of the optional things like derabbit-holing the high school can to an predictable degree, although no more than ambitions job buildings unless you have a massive teen population (and multiple smaller schools can supposedly solve that). If you mean gameplay-wise, turn the autonomy down/limit permissions for autonomous actions. The default lives up to the mod's name, and it's admittedly a bit more than I want for my regular gameplay (although it goes back up for uni).

Not sure if I've ever experienced that with the AI to know if its capable of that or not since I don't play my game like that. But that would be curious to find out, however, I do think that most, if not all Sims, would figure it out on their own. As a lot of my Sims pick up on cheating as well as with who and I had nothing to do with telling Sims to cheat in the first place. Except that one time now that I remember when my Sims got a wish to kiss another in University. Maybe there's more I don't recall since it's rare for me. Then again, it was really fun when I had one Sim who was a firefighter and had so many different romantic interests and never broke up with any of them. Eventually, he got caught but it took a long time and then after that it was extremely difficult to even get a relationship because everyone knew and ran away from him. What a heartbreaker I turned him into.

The only traits I can think of that might have an affect on a Sim's response of their partner having a child with someone else might be Absent-Minded, Commitment Issues, Dislikes Children, Insane, Loser or Unlucky. Perhaps, some of those traits could cause a Sim to know but not confront it or either be completely oblivious to it.

I'm not talking about performance drops, permissions, and redundancy, I'm talking about ongoing games imploding and becoming unplayable. Our vantage point is admittedly skewed because players don't bring us success stories like yours, they bring us games that are hosed beyond belief and we cannot help them. We do know that KW detects and deactivates NRaas code in many more far reaching instances than it does with Shooless, that's a pretty minor effect comparatively speaking, and in the cases of StoryProgression, Woohooer, and Register, does not always do so properly. World travel (Traveler mod) is also often a factor. The developer has also clearly stated that ErrorTrap should never be used by anyone, maybe she has since backed down from her original stance somewhat. But by the time we see logs from these games, the traits and dream managers for example are totally non-functioning and the game can't run without those.

Perhaps all of the players who have brought us broken games that cannot be repaired have been on older versions or have each individually done something wrong or have not taken some required tuning step for compatibility to happen, that we cannot tell. All we can do is suggest that they return to the KW developer for assistance, repeat what little we have learned about the mod's impact on ongoing games, and say that if they would like our assistance we can only provide that for ongoing game saves that have never "seen" the KW mod. Whether what we can and cannot realistically support matters to the players in question is of course up to them.