Firstly, she is having an extra marital affair. That means she is cheating on you. So, you have every right to interrogate her. She needs to give you a proper explanation for her actions. And sorry to inform you that you can’t tackle this situation legally. Because unfortunately, Indian women are an exception for adultery laws and they cannot be punished under the law for committing adultery. You can’t take action against her legally.
If you are afraid that she might file a fake domestic case against you then you can tackle that situation if you can prove your innocence. You have to gather evidence against her accusations. Then only you can be free. She can be punished for filing a fake domestic violence case against you.

Under the Section 506 of IPC, 1860:Punishment for Criminal Intimidation
The husband can file a case against his wife, claiming that she threatens him to hurt himself or his family or property. Yet again, the evidence is the only thing that can uphold his case.