I think your intentions are very noble. You clearly care a lot about both her and your kids.

But at the same time, I feel like you’ve fallen into the trap of “I must be miserable for them to be happy”. Which is a variation of “I must be miserable in order to succeed.”

If I have one regret in life, it is that I spent so much time being miserable because I thought “this is just how life is”, “I just have to wait it out”, “this is how I’ll be able to achieve my goal and then I’m allowed to be happy.” And after being miserable for a long time in a bunch of different ways, what I realized is that I’ve seen the people around me reach the same goals faster and easier because they didn’t embrace the grinding-and-suffering methodology. And really the only thing that was different was that they had different expectations - they expected to achieve their goal while being happy and having fun along the way. If a path to their goal required being miserable, they rejected that path and looked for another one, because they simply assumed that there is not just one, but many paths to achieving any goal while being happy at the same time. The problem is that if you assume the “be miserable” path is the only one that exists, then you stop looking for the other, better paths. This becomes a self-fulfilling prophecy - you believe no better path exists, so you don’t look for other options. And since you never look for other options, you never see the other options, and since you never see other options, you assume they don’t exist.

You’ve listed a bunch of things, like how your kids would have to change schools, like they are reasons you can’t separate. And I think it is reasonable to say that you don’t want your kids to have to change schools. But I feel like what you have done here is listed all these reasons like they are insurmountable obstacles to your happiness, which then implies that your happiness is impossible. I think instead you should see them as metrics for success - your ex stays in your kids lives and they don’t have to change schools and you are happy and have a loving partner.

Like, imagine that you and your ex have another kid. And for whatever reason, because this happened, your oldest kid now feels as miserable as you do now. Would you accept that? Would you say “my eldest child’s misery is the price we must pay for everyone else to be happy”? Or would you say “this is unacceptable - I will to whatever it takes to make sure all my kids are happy.” Because if you can have that mindset to ensuring your kids’ happiness, you can adopt it for your own happiness. And once you have that mindset, it’s just a matter of looking for solutions until you find the one that works best for you.