Whoa, lots and lots (and lots) to unpack here. I am not a doctor.
A few things:
- This is Reason #8,241,961 why snooping is such a bad idea. It shows mistrust which is a big problem in any relationship.
- Much of the world has been under lockdown for a lot of the last 2 months or so. Are you slapping your husband and calling him names in front of your children? I'm not seeing where you could avoid having them around while that happened. That is a truly rotten thing. Fights are one thing (not ideal, but people do fight), even physical ones (lousy but sometimes heat of passion makes someone quickly slap maybe one time -- I am distinguishing this from abuse) -- but in front of your kids? And more than once?
- And.... your kids know something's up. I can practically guarantee that. They are witness to the peaks and valleys of your marriage no matter what -- and that's got to be triply so in quarantine. Unless your children are profoundly mentally challenged or infants, they have an inkling.
- Staying together "for the sake of the children" is always a lousy idea. Seriously. The sexual revolution and the major updating in divorce laws throughout the US and other western countries didn't happen just so couples could fall back on tired old 50s tropes.
- Staying together while miserable also teaches your children that love and happiness matter a lot less than appearances and cold, hard cash. Because...
- Divorce is expensive. And time consuming. And it can be soul crushing (or liberating; your mileage may vary).
- All of that having been said, we are in weird, unprecedented times.
- I have no idea why you decided to give your husband some weird pass to go and have sex without someone else. Mistress rules? What the hell? That was a setup for a gotcha moment if I have ever seen one. Why would you do that? To prove you were so loving that you would allow yourself to be a doormat in your marriage? A botched attempt at reverse psychology? To give yourself tacit permission in case you wanted to do similar?
- And regularly asking him about whether he wanted to cheat on you? Egad, at best that's annoying.
- A 5-year affair with 40 sex videos is a recipe for blackmail. You and your husband have no idea if his affair partner will leak the videos. Or even without videos, just blab that they did this (although videos are more compelling). Why would she do that? If she wanted him back. If she wanted money. If she was vindictive. Consider how your children are going to view both of you if this all hits the fan and they still haven't been told anything.
Telehealth exists, so take advantage of it. Talk to an impartial professional about your violence, your jealousy, and your nightmares. This isn't necessarily to stay together or to leave. It's to give you tools to better handle this.
If you want to stay married, then smacking your husband has to stop yesterday. You are borderline abusive if not there already.
Regardless of your husband's behavior, you are way over half at fault here. You may not see it that way. But if I was a judge listening to you both in divorce court, I would send you to counseling and give primary custody to your husband who, despite his deception and indiscretion, at least doesn't seem to be raising a hand to anyone.