I am not a lawyer here but take it as brotherly advice -
The moment you are going to file a legal case against your husband, your husband could make the same case as reason of mental cruelty thus he can return file a divorce case. In one of ruling by Bombay high court, it has been said that any false case against hubby or in-laws are ground for divorce. I am aware that your case would be based on the facts and more and less to save your family; Same time, it should be keep in mind that any case can be turned upside-down due to lack of evidences.
Find more about this lady. If this lady is married or in a legal relationship with any other person then gather the sufficient evidences to prove her adultery. Ask her husband to do a favor and file case against your husband for adultery under section # 497. This way, you would be behind the scene and have minimum impact on your family.
Apart from that going legally on this case, would be little challenging as - Indian lower courts are not just slow.... but are very very slow & low...
