Platonic friend's dissing his wife. What does this imply?

I have a male friend who used to be a boyfriend a long time ago - there are no romantic feeling there we were more friends that anything anyways. I recently got back into contact with him - just over the internet. I'm taken aback by the rather unexpected and inappropriate dissing of of his wife of only a few years "She's a total nag but at least I knew beforehand" (before the marriage). Inappropriate but I wonder what he are really saying (I mean other than something like "I'm completely miserable"). I have a feeling he does this sort of thing all the time. Why would he think I would want to hear this?