The first thing that came to everyone's mind was, "He cheated".  But Pink is standing up for her man... well, her soon to be ex man. It's not like she needs to protect him for the sake of children. I believe her. It was probably just about two very successful people being married to their work. But in the end, only they really know what happened.
Here is what she wrote on her personal blog about the split.

Hi everybody. I wanted to reach out personally to all my fans/friends out there in the world. First and foremost, thank-you for all of your support and love, it means a lot to me right now. The most important thing for you all to know, is that Carey and I love each other so so much. This break up is not about cheating, anger, or fighting. I know it sounds like cliche bulls$*t, but we are best friends, and we will continue to be. All I know at this point, is that I want to make the best album I can, and Carey wants to do the best possible job he can with everything he has going on. He is a good man, so please support him as well. One never knows the future, but mine and Careys' just might involve beach babies and sunshine one day. Just not right now. Thanks for the concern and caring." X Miss P