Why did astronaut Mark Kelly divorce his first wife?

Who ever answered this question is pretty much mis-informed. Mark Kelly did not move out for several months after his divorce in 2005, he was seeing Gabby long before she was seeing someone else and they were never "separated" before the divorce. The only truth in the other answer is he did meet Gabby in 2003 and has 2 daughters from his former wife. People shouldn't answer personal questions about people that they do not know or know the answer to.