Not so fast! That exchange, where she begs to drop the past, sounds very heartfelt to me. People can change. And, her belief that she nearly lost you to your friend could have changed her.
Since you are at 13 weeks with the pregnancy, I imagine that you both have decided not to terminate. This is a very difficult decision. My sister had a baby after cancer treatment, and they are both doing fine. But worrying about a paternity test at this time is an ugly distraction.
You both need to go back and deal with the forgiveness and trust sections of the post sessions. And, I know how difficult it is. My husband and I got hung up on the same issues. But what they say is true, without all for supports -- commitment, trust, forgiveness, and love, the "house" that is your marriage will cave in. You are telling us that you have trouble with trust. So you have to deal with it.