I tend to agree seeing the bill at this point is pretty much useless, you know KNOW he saw her, you now KNOW he contacted her...and yes, this is a setback because he had been lying about it all along, I do know how that feels.
This isn't the end of the world though, but I believe you know that. THIS is about the stage for me when things DID begin to really turnaround, so it's up to you right now what you choose to do. If you leave, no one would blame you...you have absolute grounds, if you don't...we're behind you on that as well. I just know from my experience with my H that a similar even (with delayed honesty) was our turning point. I'm sure you DON'T have the complete truth, and you probably never will, but I think you have the important parts...if not details, can you live with the iformation you have and consider it enough of the truth to move forward...or not? Only you can answer that one. For me? I took what I knew and sat on it for a bit before making that decision and I'm glad I did.
I'm so sorry you are going through this, I'm here for ya!