Actually, I've been pondering this same issue and actually think he's been playing around since at least his campaign. Remember when he adressed that woman journalist as "sweetie"? Just the sort of thing a playboy would say (also, he admits that calling women "sweetie" is a "bad habit" of his).
I wouldn't expect to hear anything about his philandering, though. The mainstream media will cover it all up, just as they did with JFK's affairs.
As for Michelle, I don't think she's all that tough. She's bitter and angry, sure, but she knows that what Obama wants is what he'll get. Nothing she can say or do about it. Unfortunately, nasty (and ugly) Michelle will feel entitled to vent her rage on the people she finds at arm's length. Like that's anything new.