Wife makes me out to be a monster?

My wife wants to divorce, and I do not understand why. We have been married for 6 years and have three children together. She is not one to help with household duties ( I do majority of cooking, laundry, dishes, etc) and it agitates me. She spends hours online Instant Messaging another man and we fight often because of it. I have to carry out the household duties, while she flirts with another man online. She used to stay at home while I worked...I still cooked and took care of many things that she did not. Instead of thanking me for what i do, she critisizes my efforts and shows no appreciation. I am far from perfect and have a sharp tongue when i think she is being unfair or unreasonable. She brags about our life, so that isn't the problem. She brings up every wrong that I have ever done in the past and never recognizes what I do for her. There have been so many issues that I have let slide and I've tried to make it work when most anybody would have called it quits. She left me a few years ago for another woman, and still lived in my home as she was not employed. That did not work out for her, so we reconciled but continued to argue. Her own parents and family sees how she is unhelpful and unappreciative and they comment about it often. I watch the kids while she goes out with friends and don't mind if she has a good time. I don't believe that there are many husbands out there that do what I do, and I would like to understand what is wrong here. I would think most wives would appreciate the fact that their husband's iron their clothes for them every night ( I was military...I'm good at it) and wouldn't need to complain when he asks her to get up from the internet and pick out an outfit. All that being said, we are both very outspoken and I can get agitated and be an ***...but I don't do so without perceived reason. I don't want to split up my family...my children deserve better than that.