a mistress versus another mistress

Good day... I have a problem about my man. He is a married man with kids but separated for 18yrs. But we got married 14yrs ago. I knew his first wife and even personally met her in year 2001 and their kids are always visiting us and I accepted them as my own children. But the problem is my man again had a relationship with a married woman,our close family friend. I was blind that they had a love affair for 3yrs until it was known to me last 2013. And the problem became deeper when the woman filed a case against my man for psychological abuse. In her affidavit she stated that they have a secret affair. I wanted to help my man so than this girl will agree for amicable settlement. Can I file a case against this woman for concubinage? Thank you so much

I just want to help my man because I love him. If I will file a case against the woman she will bargain her case against my man if it is possible to file a case against her. Please help me. Thank you..