Like Nimir, I go by the rule of cause and effect. I use Karma in the correct context, not the new agers way.
You need to truly study Karma through the original religions that created the theory to understand it. Not your New Age section of the bookstore. It has nothing to do with cosmic forces coming down on bad people and blessing good ones. It has to do with the law of attraction. The way YOU act, feel, and think will depend on what is drawn to you. Your perception of the world and your life greatly effect your presence and future. What you do with your life will effect how quickly you reach enlightenment. You are in control of your progression or degression in life. Good Karma is the path to enlightenment. Someone can be the nicest person in the world, but could have "bad karma" due to low self esteem and a pessamistic outlook concerning their own present situation.
Just because someone breaks up with another person doesn't give them bad karma. It is their choice to do with their life as they wish. If he is a confidant, positive individual who had genuine personal reasons why he doesn't want to share his life with someone, he'll still have good karma. You can't live your life and never harm anyone emotionally. If you did, you wouldn't be living your life, but letting others run one for you. People pleasers might as well be synonymous with doormats. You can't make everyone happy and be happy yourself.