How to tell my kids we have separated

what penalty must she pay exactly? My belief is that she will pay. But not in the way you imagine. It doesn't need to be you who dishes it out. As, like you say, a circular argument!
LL

Well the penalty must suit the crime.

The view point you appear to hold is that Karma will balance itself. What comes around goes around. She will reap what she sows. I am afraid that is too simplistic. A better description of how Karma works is like this:
Ex's dad had an affair. Did not leave wife, it wasn't done in those days. Ex loved both parents and could not understand why affair happened. Decided it must be her mom's fault or it is ok, her dad did it her mom tolerated it.

Ex now believes that a person who commits adultery is the victim. That their spouse must be awful. So her father's bad Karma has been passed to his daughter. But of course she will not see this until it passes to her sons.

Karma often visits itself on the next generation. So what Karma will fall to my children? Well hopefully because I am good and decent, (but not going to be a pushover) they will end up back in balance against what their mother has passed to them.

Her emotional penalty, if any, is no long relevant to me. But, she loves money, not spending it, just having it and knowing that it is flowing in like water. It is her security blanket. I care much less about money, prefer the getting and giving of loyalty/support of anothr person. But why would I want to share the fruits of my labour with a stranger?

Her penalty then is that I will not be generous towards her. Towards the children of course. See her homeless or destitute, absolutely no way ever. It would hurt my boys. But, her having to work full time as I do. Worrying about a job when it seems uncertain, I think that is a very suitable penalty. She brought it on herself. And that is the Penalty she will suffer. Not at my hands but at her own because I don't feel any moral or emotional responsibility towards her because she felt none towards me.

To be clear LucyLou, I am not looking for vengence and I suspect we may well not be as far apart on our views at it first appears. Just a difficult subject to put in a text,
regars,
Perry