Gwen and Gavin split because one of them was having an affair.
 "Us Weekly" says that Gwen Stefani and Gavin Rossdale broke up over the NANNY. Gwen supposedly found out back in February that Gavin had been giving it to her for three years!  Her name is Mindy Mann, and she'd been exchanging texts and nude photos with Gavin. Another nanny found out and ratted Mindy out to Gwen.

Mindy was fired, but Gavin spent the next several months claiming it was just "flirtation". He finally fessed up, and that's when she decided to leave him. What made it worse is that Mindy had worked for them since 2008, and Gwen trusted her.

The timeline works, because during a radio interview earlier this week, Gwen said, quote, "Everybody knows that my life blew up last February."