I can't diagnose your issue, but I think that you should see someone about this. We all have a tendency to selfish reactions sometimes, but to me what you're describing seems outside of the regular range in terms of your inability to react to others' pain in a kind way and feel sympathy for them, even though you recognize that this is the expected reaction. It is a good first step that you recognize this as a problem in yourself that you want to change. I think the next step would be to see a professional to find out what is causing it.