A gentleman was complaining about being married to someone who was very negative and he felt miserable in the marriage, he just wanted out but loves his children. Here was my suggestion:
First of all I would stop focusing on how negative she is, the more you do that the more negative she will be. Especially if you point it out to her, she will just defend why she is the way she is or say she’s not negative. It is natural to defend yourself when attacked, unless you learn some techniques to handle the situation in a different manner.

I would get the movie The Secret at the site TheSecret.TV/ the movie is excellent and teaches about the law of attraction- what we focus on we get more of. I strongly suggest you watch it, with her would be great – it sounds like you both could use the message it has. I also suggest you write a gratitude list everyday, with a minimum of 6 things that you presently enjoy in your life. This should be a different list every day. An example: I am so grateful for my children, having a hot shower this morning, the coffee I had at breakfast, how well my wife takes are of our children, my car that gets me safely to work every day, my home. I would also write a list of your wife’s positive aspects, and I am sure she has some. When you focus on the positive aspects of someone you tend to attract more things to appreciate in them when you are around them.

These suggestions would be the first ones I would teach to help this man focus on what he chooses to experience rather than focus on the “reality” of how miserable he feels.  When you take steps to “feel better” you become a match to other situations and outcomes that feel good!