They didn't know either. When her best friend found out she is the one that called him on it first. She (the friend) found out through another acquantance whom she was telling about him and Amber. This person said he knew Scott and that he was married. That is when it all started falling into place. Scott told Amber he had lost his wife. Only problem, he told her that on Dec. 9th and he really didn't "lose" his wife until the 24th (date?). That shows the premeditation of his actions right there.
Strange, you would think that a friend would try to get to know the individuals they were setting up with each other better. Before they started trying to mix each other up in their respective lives.