Husband is cheating on me and making our kids lie about it.

I'm 38 we've been married for 20 years . We have 3 beautiful children 17, 11 & 8 they get great grades, good at sports we even have a beautiful dog that people love! We were a family that people would look at and would never think there was anything wrong. Abut 6 years ago I found out my husband was cheating on me. I did the whole phone log thing I pulled his calls narrowed them down to the one, got into his voicemail. I found out where the girl lived and when he didn't come back one night I went there to her building and waited until he came out. That was ugly he finally admitted to cheating we worked through it, it took almost a year for me to trust him again. I never saw or heard from the girl again he promised that it was over & that was it. He never gave me a a reason not to trust him after that. Fast forward 6 years this woman moved 2 blocks away from my home. One day she is yelling outside my house for him to come down that his "baby momma" is out side she has had 2 kids over the past years and says he is the dad!when I heard her voice I got a huge lump in my throat and my knees went weak. I literally couldn't stand I kept feeling like I was going to fall. Anyway he tells me some bullshit story that he hasn't seen her in all these years she is crazy, he denied it all, etc... this was a year ago. I'm out with my 11 year old daughter yesterday she turns to me and says "Mommy I have to tell you something but I'm afraid to say anything" I finally get it out of her, that on Wednesday December 27th two days after Christmas The woman & her two kids came over to my house while I was at work to have a play date with my younger daughter. They came over at 4 pm and left at 7 pm (I was at work until 9pm) The kids played with my younger daughter and my husband and this woman sat on opposite sides of the couch and watched the movie IT and smoked weed, the little girl called my husband daddy she said. I said what did your father say when she called him daddy she said nothing he laughed and said to my kids "she's silly" she is just kidding! My children were sworn to secrecy and told that if you tell your mother she will make me leave I''ll have no where else to live your mom doesn't like this woman and she will get really mad. So any normal person would say why can't we say anything? My 11 year old says so why are they here who are they, my husband responds " Shut the **** up"! After they leave my 8 year old asks to have a play date again of course as any kids would usually do my husband told her no that this was a one time thing and it wont happen again. After that bomb shell my daughter tells me that in October he took the 2 younger kids to her house so he could get her hair braided and of course was practically threatened to keep this a secret. I promised my daughter that I wouldn't say anything she is scared that we will get a divorce. But there is no way in hell I can't blow this up. I do not want to reconcile. By the way I didn't mention I am the sole breadwinner he hasn't worked in a few years so I have a free loading bum, I also found out that this woman has no job she sits home all day collecting SSI and apparently smoking weed. This is over apparently. But I am in shock I cannot wrap my head around this. It is one thing to have a affair, to even get this mistress pregnant. But why bring them to my house in front of my children. Now when I am home we are a family we get along we laugh kiss, watch movies together with the kids as a family we even do family game night! So I don't even know where to start. Please I am desperate and too ashamed to talk to anyone I know. Why would he involve my kids in my home. He wont leave easily I know this will be hard to get him out. I am his security blanket & apparently I am a meal ticket also. Please anyone comments suggestions any advice