I'm sad for you. I wonder if your wife is regretting some things now?? Our poly journey started with me falling in love with our neighbor and downplaying it -- i.e lying. I did confess everything, which led us to try poly. But I believe that, like you, my husband never got over the pain of me cheating. He got a girlfriend about 6 months after we opened the marriage and then HE started lying to ME. He feels justified in everything he does now. He downplays his relationship with her, although he is treating me as a total secondary (if that) and took his relationship with her farther than it was ever expected to go. He met her parents after only about a week, and he sent pictures of her and her kids to his mother! Well this is my story, but I can only speak from my own experience. I find it admirable that at least you are being upfront about your feelings now and admitting your girlfriend's emotional well being trumps your wife's. Wouldn't it really be better for your daughter if you both had authentic relationships and quit propping up the wounded thing that is your marriage?? It's no crime to move on.
I thoroughly understand the economics of your situation. Ours is dire too. But it's not worth the emotional expense of staying in a broken marriage. I'm looking for a way out, myself.
I commend you for coming here and owning up to your feelings and actions. That takes courage. You sound like a man of integrity. Show your daughter sometimes the respectable thing to do is admit when it's time to make a healthy change. You all deserve respect. I don't see much hope for that if you continue on living as you are.