A wife wants to know if she can file a case against the husband and his girlfriend.
As per your query , the first step is to file a petition in the family court for Divorce is on the grounds of divorce under Section 13(1)(a) under Hindu Marriage Act, 1955. The Court will then send the summons and call the husband to the family court for first hearing and on the same day you two will be sent for counselling. The Counselling sessions are mandatory for every divorce couple as the objective of the family courts are to maintain the sancity of marriage. After 2 or 3 counselling sessions spread out over a period of 3-4 months, the counsellor may send a negative report to the Judge stating that conciliation is not possible and that is when the trial begins.
You must have all the evidences regarding your husband adultery, you can also mention in the petition the name of the person who hs is in an adulterous relationship with and that person can be called upon for cross-examination to prove adultery.
Any evidences such as hotel bills, photographs, video clips, audio recordings etc or any circumstancial evidences will help strengthen the case.
With regards to girlfriend , you can not file a case against her as Section 497 of the Indian Penal Code , 1860 has been struck down. However , even if it was not struck down it related only to men and not women.
Reference: Section 497 in The Indian Penal Code
497. Adultery.ÑWhoever has sexual intercourse with a person who is and whom he knows or has reason to believe to be the wife of another man, without the consent or connivance of that man, such sexual intercourse not amounting to the offence of rape, is guilty of the offence of adultery, and shall be punished with imprisonment of either description for a term which may extend to five years, or with fine, or with both. In such case the wife shall not be punishable as an abettor.