Scott Peterson admitted he had an affair last year before his pregnant wife vanished, and claimed he told her about it.He also has previously denied killing his wife.'The affair was not a positive, obviously..but it was not something we weren't dealing with,' Peterson told ABC News Good Morning America in an interview broadcast Tuesday.'It wasn't anything that could break up apart.'Laci Peterson 27, disappeared on Christmas Eve from her home in Modesto, CA.Scott Peterson 30, told police he was fishing at the Berkley marina at the time, and that his wife had planned to take her dog for a walk...