Emotionally this is a terrible situation, but it sounds to me that legally you are actually in a very favorable situation if you play your cards right.
A disclaimer - following my advice will most likely get you divorced, but my views are that:
a. It is generally preferable to be happily divorced than miserably married, and always better to be happily divorced rather than miserably divorced.
b. You will be much more successful if you only try to control your actions that are under your control, and not try to control your WW actions or outcomes that are not under your control.
c. You really cant control the outcome of whether you stay married or get divorced, but you have a lot of control whether you are happy or miserable in either outcome.
d. The actions you need to take to be happy with whatever outcome arises are basically the same whether that outcome ends up being divorce or reconciliation, and it all boils down to putting yourself in the strongest possible position in terms of finances, custody, emotions and health.
So, to that end I have a checklist of actions I would advise you to boldly undertake if you were consulting with me: 1. Keep a journal documenting ever single parenting action you take. There should be a full entry every day, even if it is just "texted kids at their mom's"
2. Visit many different attorneys ASAP, especially any you can find with a "shark" reputation. You will get different opinions, you will also block your WW from hiring any of these sharks. Most nightmare divorces boil down to a nightmare lawyer.
3. File for divorce with primary custody and support. Get your older kids to write down their preference on living with you. Don't move out until you have papers filed, or you have your lawyer's blessing in writing. As to filing under adultery, that depends on your jurisdiction and the judge. Where I am it is a great advantage most of the time, but other places it is just extra legal costs.
4. I don't advocate full blown exposure like you see on other sites, but I strongly advise you to not keep her affair a secret from anyone. You must understand that she has been building a case against you for many months, and you need support from people who know the truth. Also, I believe you have a moral obligation to tell OM's wife.
5. Show your cards on exposing to her and OM's employer, keep this option as leverage.
6. Spend time with your kids, friends, family. Look for support. Work out to exhaustion every day using HIIT and heavy weights. Think about where you might want to live/move, change your hair style and buy new clothes that are nicer and younger than you currently wear, and smile at the check-out girl.
7. Don't send any communications to anyone that you don't want read aloud in court. And don't argue the case or any sort of logic with your WW, it will accomplish nothing and only do you harm.
8. Keep the car!
If you do all this, and do it right now while your WW is still infatuated with OM then this process will be wife will not even notice you leave, or she will find herself with the rug pulled out from under her and suddenly you look like the better options.
