In Vermont, one of the grounds for divorce is adultery. In 30 years of practice, I have never seen a judge rule that divorce was granted on the grounds of adultery. This is because in Vermont a divorce can be granted on the grounds that the parties “have lived separate and apart for six consecutive months, and the likelihood of resuming marital relations is not reasonably probable.” This is simple to prove, and parties generally are not able to get into court for a final hearing for at least six months after they have filed anyway.
Adultery can be a factor, however, in property division. It is the 12th factor that the court can consider in dividing up marital property. It is called the “merits of the parties”. Here Vermont Family Courts do ocassionally consider adultery as a factor; particularly when the adultery is egregious: ocurring over a period of years, for example. However, as a practical matter, it is, in my experience, rarely a large enough factor to have any significant effect on the amount of property the parties receive.
So for the courts, adultery is generally not important.
By the way, the courts do not consider intimate relations with another person after the parties have separated to be a factor at all under the “merits of the parties”. In other words, the courts do not seem to consider such a relationship to be adulterous.
Adultery does matter, both before and after the separation, to the parties. And this can have an adverse effect on the ability of the parties to reach an agreement, and can certainly raise litigation costs. If your spouse is angry because you are now living with another person, your spouse will more likely fight over the toaster and the dog–and, more importantly, over the children and their contact with you.
In conclusion, then, my advice is to hold off on any new relationship during the pendency of the divorce. It will make things go smoother, be less expensive and time consuming, and be better for the kids, who are already going through enough trauma with their parents’ separation.