Fiancé lied 3rd update!!!!!!

My fiancé has been acting strangle for that past year really... I thought I was crazy so I just ignored it.  Yesterday I got a text from someone, and it was a girl claiming my fiancé was also her boyfriend.  She asked to meet up with me, so we met at a Starbucks.  She is 6 months pregnant with his child... She showed me pictures, text messages, call logs etc... To prove it was his she called and let me listen in.  It's all true.  He doesn't know that I know, and I don't know how to confront him.  She was very apologetic and she thinks we should surprise him but her coming over and both of us standing in the living room when he comes home from work.  I am torn a part.  But I'm also mad at him, so is she.  Ladies, what would you do?  
So, when he got home we were sitting down in the couch watching how to get away with murder, lol.  He froze and actually tripped, which made it better.  He apologized and try to deny her, but I told him to save his breath.  I Nicely packed all of this things in trash bags and put them at the end of the driveway for easy grabs.  He left mad as hell.  But now I have a new friend! 
2nd update: she did not know about me until 2 weeks ago, but she confirmed it last week.  She left him like I did, and I will remain friends with her.  
Final update*
We did not have a wedding date set, and for everyone saying I can't trust this woman blah blah blah, you don't know much about this situation between us.  I WILL continue to remain friends with her.  Why??  Because she worked up the NERVE to tell me, she knew she was the "other" woman in the relationship.  As for him, he has texted and called, but I changed the locks on MY house and am selling the ring.  Already have a taker!!!!  I am choosing to remain anonymous because I don't want to get judged or attacked on here.  I had a feeling this would become a popular post, so that's why I am anonymous.  Thank you all for your support, we are best friends and have a lot on common.  Thank you lovely ladies for the advice!!!!