OTL, the Edwards affair news came in waves, but it wasn't what ended his campaign, and wasn't really considered a verifiable story by non-tabloid media while he was a viable candidate.
As the primary season progressed and Obama and Clinton went head to head, Edwards' vote share declined from losses, but he wasn't considered a finished as a politician. It wasn't until he was confronted outside a hotel going to meet Hunter and the baby in July that he was dead to rights on the affair. After Iowa, Edwards' delegate numbers went into a death spiral, and he stopped campaigning after Super Tuesday. After that, both campaigns sought his endorsement, with Clinton's offering a state by state unity tour and discussions of a role in the administration, and Obama's being less transactional, but offering a primetime slot at the convention. Edwards ended up endorsing Obama in May. So, you could plausibly get him the nomination and then have the affair spill into mainstream news.