Re: Here goes nothing... (sorry, very long)
Be prepared for any outcome. @MMJEAN could very well be correct. She might have never envisioned life without you. Her "I love you" texts might be sincere. She just was thinking like a child, enjoying the moment in her "open marriage" and never imagining the consequences of getting caught. Now she stands to lose her husband, friend (who stimulated her intellectually), her children (half time), her house, and half of her assets.
Your job is to bring this reality home by striking hard and fast. File for divorce. DNA the children in her presence. Arrange an STD test in her presence. Move into a different room and put a deadbolt on the door. Expose the affair to all of her family, your family and anyone who ever had respect for her. Inform the other man's wife even if we think she's written him off (you never know what their current relationship is, or if she was even an alcoholic). Start an anonymous blog to post your experiences and make sure she sees it. Do the 180. Be business-like in your dealings with her. Polite, but only discussing matters related to the children and division of assets. Make a schedule for watching the children. When it's her turn to watch them, you spend most of your time out of the house. She doesn't need to know where you're going or when you'll be back. Have her verbally promise, under threat of legal consequences, that she will not have dates with other men (and yes, use the term "other men", plural) either outside the home or inside the home, while it is her turn to take care of the children.
As time passes, you'll have a clearer idea of whether you want to reconcile and whether she's willing to make EVERY sacrifice necessary. If so, you can stop the divorce proceedings at any time.