I first saw reference to this showing up in the National Equirer and discounted it. But this is in the UK Daily Mail. They say that the couple have been fighting and hint at a Presidential affair. I seriously doubt that sex has any thing to do with it. I think the two of them have just as much sex as they want with whomever they want.
After seeing some of Michelle’s expressions when dealing with Barack I would say it’s more likely that he has embarrassed her and she doesn’t like it.
We’re talking about a marriage between two narcissists. Neither cares for anything but themselves. He is a good-time guy who enjoys his comforts foremost. And he seems to be protected by staff from any negative press. She, on the other hand, is driven by ideology. Anything that gets in the way of achieving those is dealt with severely. Any time he does something that makes her look foolish he hears about it.
Here is another link to the story in the Daily Mail.