I am very sorry that you've experienced all of this, and even sorrier for the children involved.

Since you were never bound by a legal contract of marriage, it's more a matter of custody and visitation.  And, this is getting down to the facts of the situation, not the emotions.

Managing the emotions is going to take time, work, and some serious digging in the dirt.  Personal work for you.  What begins as "...what s/he did to me...." will come around to "....how I can make myself safe, secure, and confident."  You might want to consider counseling therapy, but that will have to be a personal choice.  Two blog sites that discuss betrayal and so forth:

www.familyarrested.com

www.180rule.com

As far as the living arrangements and custody goes, the only contact required is with regard to the child that you share, in common.  The step-child is not your legal responsibility, although you may have a strong emotional bond.  Sadly, Family Courts often drop the ball on this particular issue, so you can file for formal visitation/custody arrangements.  Speaking with her about anything other than the needs of your child is out of the question - don't allow it, and don't try to educate her on what she's done to you.  If she cared, she would have alerted you to issues before engaging in whatever she was doing.  Be assertive in your language.  For example, "I'm only discussing our child's needs, right now," and STICK TO IT.

Then..........keep those children out of all adult issues.  That means no discussion of bills, child support, or what she's done, etc.  Keep those children OUT of the adult issues, and you are allowed to address it in that manner, "I know that you're upset, but none of this is YOUR fault, and these are issues that are between your mother and me." 

Unfortunately, adults have no inkling of the horrific damages that their actions cause for the children who are in their care.  So, armed with that information, I promise that you will be okay.  What you believe that you "love" might not ever have existed - it may have been a "fantasy" that you loved.  And, it's possible that you might not be aware of issue that you might have, yourself.  So, this could be a wonderful (yes, "wonderful") opportunity for you to learn about yourself.  If you read my CureZone blog, "Coping With Betrayal," you can see, in words, a 3 year transformation that I've personally experienced when my marriage ended.

You're okay, and you're going to get through this.  Best wishes to you

You know, I thought I'd never tell it anyone but here I found your question. Believe it or not, this is not the worst feeling. I can tell you, as I have similar situation. He and she. Love of my life and my best friend. She knows, how much he is in agony about her, but she doesn't like him as a man, they've been friends since childhood. Not he, nor she knows about my feelings. He makes stupid things, tries to finish his life. And all that could just kill the three of us one day. Well, kill me for sure. But you know what? I don't let in all the pain and thoughts, I just said to myself "I must survive" and I move on. Maybe, one day we'll be together. Maybe, he'll be as stupid as he's at present. Life's mine, I should live it and be happy. There is another "maybe" - maybe I'll find somebody and forget all this. Really, try meeting new people, that heals. The Internet may be the first step - https://kovla.com/datings/us/annapolis/ Good luck!