My Advice as per your gist:
1. You can file a complaint against the said person for committing adultery in the nearby police station.
2. Collect proper evidence which denote adultery was committed.
3. Evidence you have to collect in cases of adultery: Circumstantial evidence, evidence of visit to houses of ill-repute,
admissions made In previous proceedings,
confessions and admissions of the parties. Mere suspicion is not sufficient.
4. Once you make complaint to the police, they will start their investigation without arresting the concerned person as it’s a bailable offence. If you don’t have proper evidence then you may face difficulties in registration of FIR through police. In such a situation you then have to approach the courts of metropolitan magistrate for registration of FIR under section 156(3) Crpc with all supporting evidence.
5. Parallel to all this you can ask your wife for mutual divorce without creating disturbances in your life and your daughters lives. If she opts for this then proceed for mutual divorce which will take 6 months for a divorce decree.
5. If she does not agree Then file a case for divorce on grounds of adultery as the Hindu Marraige Act gives right to husband to allege his wife for commission of adultery and take that as a ground for seeking divorce.
As your marraige span is long and you have grown up daughters, you need to first think about the pros and cons of each and every step you take. This is the time you’ll initiate and the way you initiate will prolong till the end. My response is pertaining to what actions you can take, but you know the consequences well.
Any more assistance as per your idiology please feel free to consult.