This girl needs to own up to her boyfriend that she slept with another guy. She then needs to break it to him that she is pregnant, but making it very clear at this stage that the father is unknown, and that is will find out as soon as possible to put everyone's minds at peace. Will, it is absolutely not your place to be telling your friend that you got his girlfriend pregnant, that is a surefire recipe for disaster. It is their relationship, and your place in it right now is as an unwanted anomaly. Be the grey man, keep a low profile and don't do anything rash. You are going to have to come to terms with the fact that you have likely done irreparable damage to your relationship with both your male and female friend.
You are going to have some hard choices ahead, and I wish you luck with that.
Also, congratulations on siring progeny.
Ed