What Jade told Adam was this: "In the beginning, I thought I was pregnant. I had all these symptoms." Then, after Adam asked if she took a pregnancy test, she told him she was certain she was pregnant and did not want to see the proof, because if she saw the proof it would make it real, and that terrified her. Adam asked her what happened once she found out there was no baby, and Jade responded by telling Adam, "I wanted to hold on to the fantasy for a little while longer. I had just gotten use to the idea of being someone's mom, and sharing that with Will."
So, in all honesty, Jade didn't tell him the whole truth, and she mentioned nothing at all about how she tried to set Gwen up at the library. What I really want to happen is, later, I hope Adam goes to Will and asks him for the whole truth about Jade's fake pregnancy, and I hope he tells him how she tried to set Gwen up too, and then I would like to see Adam go straight to Jade and tell her all about it! :D But, since I only write the updates and not the show, I can't make that happen.