Pick your battles wisely.
Believe it or not, in most states, her leaving you is irrelevant to the cost share.

So, if you are going to argue things, why not focus on the cc debt and NOT the son? Just saying it looks lousy, and will be remembered forever, and frankly, I think the son's costs are a lot less than the other debts that are mounting. I cannot imagine splitting the costs of diapers being an insurmountable problem. And Alamo, arguing about the costs of the diapers and son, well it just sounds bad. IDK how else to say that. I understand she's gone back on her word and that bugs you. Maybe you can say, calmly, almost with curiousity, that you wanted to re-cap the "old" agreement and make sure you were not having an amnesia attack (or took some crazy pills that made you forget the agreed upon terms) but if you can almost make it funny, like "I could have sworn we had an agreement in which you would pay this X, and I would pay that Y. I am asking to make sure I didn't have an infarct in my brain, and I am not necessarily arguing it. Just want to make sure I heard what I thought I heard and so, this is a RE-NEGOTIATION, right?"

I am married to an MD. I don't recall if your w is in her residency now or still in med school. Either way, her school loans are huge and climbing. I pray all those debts are in HER name.

So, how'd you guys get through that time with her in school and you not working? (BTW, NO MED STUDENT HOLDS DOWN MORE THAN A PART TIME JOB...I'm not sure if you meant to imply that she was a slacker for only working part time while in school, but med school is incredibly time consuming. She's no slacker.)

I've witnessed the whole journey of becoming an MD, AND my h was first a DVM (veterinarian) and we were m for that too, and then I went to law school. I got to be there for all the "Fun" times AND we had 2 of our 3 children 8 weeks before med school began and in his 3rd year, we had our 2nd child. (The 3rd scrapper came years later).

I can say with an informed opinion, that By far, his med school/residency was the worst & most relentlessly demanding experience of the three. (If he ever says he wants to be a dentist, I'll strangle him cry )

Depending on the stage of training she's in, you know that when her income jumps, you can renegotiate the support payments. She won't get alimony from you unless you are a millionaire, and the CS you pay if she has more custody, will be based on your income. I'd be surprised if you don't get half OR MORE custody, given what her schedule will be like. In fact, I'm betting you could get custody of them more if you have regular nights OFF.

It just sounds as if you are letting emotions color this. Her decision to leave is not financially relevant in the eyes of the court, except possibly for the transportation costs for the son. Is she going out of state for her residency? Again, I am guessing at the stage of training she's in. Make sure you get a clause saying you want the son close by.

Do you understand why the person who gets primary custody of the child usually spends more, in unseen ways? I think you're so upset right now that you are not objective. I understand that. But it does not help your position.

While I don't want you to sign anything that hurts your interests down the road,
I do have 2 questions for you to bear in mind always...

What is your long term goal here? Will fighting about money now, help you towards your goal, or push you farther away from it?