Legal action against mistress

Hi atty., good evening. I have consulted friends and other people but I think this is about time to do legal actions about my situation. I'm a mother of 3 beautiful kids and my husband and I are married for 11 years. I must say that we had a very rough married life. He has cheated on me on the earlier years of our marriage and I admit that I also had an affair just recently. When he found out about the guy, he used it against me. Nakipaghiwalay sya with the blame on me only to find out he's also having an affair. I want to fix our family for the sake of my children that's why I want to make things right this time. I already talked to the mistress' family but it seems they just took it for granted. My husband and his mistress keeps on going to a motel for 4 months now. He's spending more time with his mistress than his kids. My kids are so affected with our situation and I'll do anything not to let that mistress ruin our family. I want to file a legal action against her, please advise. That mistress knows about the info of my ex-guy and I know she will take it against me. Please help me what to do. I'm doing this for my children. Would appreciate your advices regarding my concern. Thank you.

Just to add, that mistress is acting now as a wife. My husbands family and friends still want our marriage to be fixed. The mistress is jobless, and the way I see it, she's totally manipulating my husband to the point that he has no time for his kids anymore. Our common friends know her because she was their classmate in high school. Our friends fully understand why I had an affair because they've witnessed how I was treated by my husband for so many years now. They didn't get mad at me at all nor his family. My children are the one's affected by our situation. I know my husband will not make ways to bring her back if the mistress separates with my husband. The only way I can think of is to file legal action against her. Hope you can help me. Thanks.