My advice: focus on one potential major life change at a time.
IME, the times when I have been most tempted to make a major change ("let's quit and move abroad!") have been when something is out of whack that I am not dealing with -- it's much easier to persuade yourself that life will be better if you just make XYZ simple/obvious change, rather than deal with the hard/sticky/hurtful/nasty emotional stuff. The problem is that this leads to over-estimating how green the grass is on the other side -- and then when you do get there, you're still stuck with the hard/sticky/hurtful/nasty emotional stuff that you've been so studiously avoiding.
You have major, hard life stuff going on. You are contemplating divorce. You have a young child. You are already feeling overwhelmed and have just added more work hours to your day. You are looking at the end of the gravy train in another year or two. That is a lot.
Luckily, you are also trained to think rationally. So tackle this like you would any major new matter: break it down into pieces, and then prioritize those pieces.
Priority #1: your health. If you are stressed and overwhelmed, why oh why are you working more? Go back to 85% -- you make plenty of money to get by, you don't need the extra 15%. And for the love of Pete, start saying no. What are they going to do, fire you? You've already said that's coming in a year or two anyway, so take full advantage of knowing that you are on the "out" version of the "up or out" path.
Priority #2: your family. Deal with your spouse; go to counseling; file for divorce if needed. Fish or cut bait. This is muddling your thoughts on everything -- it is flat-out impossible to make a logical decision when your every day is filled with stress and emotion. Just ask the recent widow my family bought our home from -- she has regretted selling the family home for the past 30+ years since. Use your 85% status to take the time you need to get your family straight, one way or the other.
Priority #3: your career. You are correct that you need to consider your long-term options -- you just don't need to do that right now. You said yourself you have a year or two left, and you're clearly not starting school while still doing your current insane job, so use that time to investigate all your options. Look for other, lower-stress legal jobs -- maybe a niche firm in an area you are interested in (that's what I do -- work is more enjoyable, and the super-busy times are offset by less-busy times), maybe a government job, maybe an in-house job.* What do those pay? Anything sound interesting? And look at your other nursing options -- paying $100K to chase a career that pays less than that, plus another $80K in living costs for the year you can't work, is not a good financial option, so figure out ways to do it cheaper. Talk to friends in the profession, try to make contacts in the community who will tell you the good/bad/ugly. Once you have 1 and 2 under control, you will be in a better position to evaluate whether there is something about nursing itself that draws you and is worth the financial hit, or whether it just seemed like a good escape and isn't so awesome in the cold light of day.
And while you are doing all of that, prepare yourself financially. That means: live on your anticipated future salary -- and put the extra savings into an account to pay your tuition and living costs. Because my one rule is that there is no way on God's green earth that you should finance a degree that is going to reduce your salary. And practically speaking, if you need $80K to get by now, and that's what your desired career offers, then how are you going to manage to pay off that six-figures of debt on top of it all? Are you going to have to jump on overtime and weekend shifts just to pay the debt -- thus putting yourself right back into the crazy lifestyle you're trying to avoid? Will you be stuck in NYC because of a custody decree, or will you be able to move to some better geographic arbitrage -- and how do the finances work under both options? And how many more years will you have to work if you take on $100K in debt + a year of $80K living costs without income, vs. $180K in the market? Is it worth it?
In short, before you do make a big jump, you need to know what you're getting into and be sure you will be happy with the lifestyle you will be able to afford. So isn't it nice that you have a year or two to figure that out?
Finally: breathe. You have options and time. You can do this. Good luck, and I am sorry you are dealing with so much at once.
*I assume you work at a big firm. So talk to them. Law firms love placing associates with their clients, because they think it helps build tighter client relationships -- we do that all the time with associates who aren't working out for one reason or another.
