36,
She's playing mind-games. It is simple role reversal. She probably suspects that you may be considering divorce, which puts her in a position of weakness, so she turns it around, and creates a scenario in which she has the power to decide. It's all about that 'P' word again: power.
What she did reminds me of those scenes in a movie where a boss and an employee have an argument, and the boss finally snaps and says, "That's it! You're fired!", and the employee responds, "You can't fire me, because I quit!" It's all just a power play. You can't divorce me, because I'm divorcing you.
To add to the impression of power, she frames it as if she has a street-gang behind her to back her up. There is power in numbers, isn't there? Mess with me, and you mess with my whole crew.
Also, by taking the stance that she did, she makes you out to be the bad seed who deserves to be dumped, as if you are not good enough for her. She has taken the position she is in, reversed it, and put you in her place, and her in your place.
It is totally unproductive, but there does seem to be a dark side to her ego that keeps surfacing. I struggle to see what she hoped to achieve by that outburst, unless she thinks that by taking that stance she might make you get on your knees, apologise, promise to try harder in future, and beg her to give you another chance. Or, maybe she was fishing, to see what you would say about divorce.
Have you heard the old saying, "Never negotiate from a position of weakness"? Why do you think your wife keeps creating one ridiculous scenario after another in which she is the one in a position of power?
The best way to handle outbursts like that is to have a simple response prepared that shuts down any further discussion. "I'm not here to discuss that" is a good one to keep repeating, because it reminds you not to engage when she tries to hijack a discussion and control it, and it really annoys people if you keep repeating it calmly and casually!
"My friends say I should divorce you".
"I'm not here to discuss that".
"My friends say you're an a**hole".
"I'm not here to discuss that".
"Well I am!"
"I'm here to discuss the business about xyz. If you don't want to discuss that, I can leave now. So are you going to discuss xyz, or shall I go now. It's your choice".
Be calm, be casual, but be firm. Your wife seems to want to dominate or control any situation she is in with you, and this latest outburst is as predictable and inevitable as all the others. She wants the upper hand, she wants to be in the position of power, she wants to be the one in control.
It's all quite odd, but maybe even the affair was an exercise in power and being the one in control. Since discovery, she seems to have had no remorse, but plenty of venom because you spoilt her fun, and she still seems to be attacking you for that. It's the complete opposite of what most waywards do after discovery, but your wife does seem to have an ego that is badly out of control, and a huge sense of entitlement.
I am sorry that yet another meeting was blighted by melodrama, but consider it another lesson learnt. Plan what you want to discuss, maybe take a list with bullet points, and have your stock answer prepared in case your wife attempts to hijack the discussion and steer it away from the business at hand.
You deserve do much better than this after 36 years.