Some states, such as New Jersey, call this a divorce from bed and board.
If a married but separated man takes a woman out for dinner, but drops her off at the end of the evening and goes his own way, it’s generally not adultery. If he dates that woman repeatedly and they begin spending time together in each other’s homes, this can open the door for his spouse to claim the affair is adulterous because sexual contact might be taking place.
In some states, adultery is a crime, although it is rarely prosecuted.
In states that still recognize fault-based divorces, adultery has more of an impact.
If a man begins dating during a legal separation in one of these states, and if his wife can prove that the relationship is sexual in nature, she can usually file for divorce on grounds of adultery.
This can affect issues of property distribution and alimony.