So many reasons. The main one, I think, is that he is a narcissist. Everything else flows from that. The constant need to blame me for everything that ever goes "wrong." The accusation that I "don't do anything" towards cleaning the house. (For the record, yes, the house is a wreck. Neither of us does much to fix that. But his overblown idea that he does "everything" is right in line with the narcissistic personality disorder.) His complete refusal to listen. His rude, condescending, mocking attitude and words whenever I try to talk to him about our marital issues. His repeating things over and over and over unless/until you concede that the thought was brilliant just so you don't have to listen to it again. His constant bragging about how great he is at his job (teaching sixth grade) mixed in with occasional disturbing stories about how he said something mean to some kid, "but I told him they'd never believe him because I'm the teacher so they'll believe me." Ugh. What did I ever see in this guy?
God help me. Divorce is hell. Divorcing a narcissist is hell on steroids.