Your case is about adultery. Adultery is voluntary sexual intercourse between a married person and a person who is not his or her spouse. Adultery is extramarital sex that is considered reprehensible for social, religious, moral or legal reasons. As you said, if your wife and her boss are having an affair, then she is clearly cheating on you
Prior to 2018, Section 497 IPC criminalised adultery by making a man who has sexual intercourse with another’s wife guilty. Adultery was punishable with a maximum imprisonment of five years. Women, including consenting parties, were exempt from prosecution.
After much back and forth, the 2018 Supreme Court judgement decriminalised Section 497 of the IPC, which criminalised adultery and treated a woman only as her husband’s property, taking away her ability to make decisions.
Unfortunately, you cannot take legal action against her for adultery, but adultery is still a valid ground for divorce. Before you think of the above measures, I would advise you to discuss them with your wife and her boss and then take action.