You have quite a problem because it sounds like your wife does not take commitment all that seriously. I know I'm basing this on scant information, but it also sounds like she is unusually quick to entertain divorce as an option - sort of like, at the drop of a hat. This could be the result of immaturity. Or it could be due to her having a mean streak whereby she thinks throwing out this threat gives her more leverage in the relationship. That's not a nice way to manage conflict.

I say "immature" because what we all need to learn in a marriage or committed partnership is that there will be ups and downs. Anyone we live with is going to get on our nerves from time to time. No two people will be always on the same page. Maybe she got married, thinking it would be one, long continuous honeymoon. The frequent threatening and then changing her mind strikes me as childish.

How you deal with this is the big question, and I don't know that I have any great suggestions. She's thinking that the grass looks greener on the other side of the street, which it can do, although usually that's an illusion. Counseling might be worth a try. I don't think that will change her coping pattern. But I would leave no stone unturned in trying to prevent divorce. It sounds like you guys have intervals wherein you do have success in this marriage.

You haven't said whether or not she has stated exactly what her big beef is. Maybe you could discuss a bit about what issues seem to be in play here.

I believe a couple has an obligation to young children to strive hard as they can to give the kids a stable home. Divorce is awful for kids as young as yours. There are cases where divorce is less awful than staying married, especially where chronic infidelity, domestic violence, heavy substance abuse, or extreme financial irresponsibility is going on. I'm not hearing any of that in the case of your marriage. Maybe she just gets bored. Meeting commitment and handling the mundane responsibilities of everyday life does get boring. That's reality for all of us.

I don't think ADHD is the main driver of your wife's mood shifts or marital dissatisfaction. I suspect she has unrealistic expectations. The threats she keeps throwing out are indeed driving some anxiety in your mind. Maybe you need to be a little less chill. She may be just trying to get a rise out of you. Sometimes getting upset can be healthy, but that's tricky.

I've not offered much advice, but maybe I've thrown out some ideas on defining the problem better. Divorce, IMHO, is somewhat tragic. Especially for kids. I hope it doesn't come to that. However, if she seems serious, quietly get yourself some legal counsel. (You need not even tell her about you doing that.) I've heard that attorneys often advise men against leaving the home because that can be interpreted as you abandoning the marriage. You have jointly owned assets and need to protect your stake in those. I hope this upset settles down.