I want custody of my nephew

Thank you for the question. Issues of custody are complex. As a general matter, the rights of biological parents supersede that of any other relatives. However, there are instances where this is not necessarily the case. In your situation, I think it is important that you consult with any attorney regarding whether or not you would have standing to make an application for custody of your nephew, or if an agreement can be worked out with his father such that he would agree to allow your nephew to live with you. If your nephew's living situation rises to the level of neglect, then there are other means with which to address the situation. 

While you can only become your nephew's guardian if his parents lose their parental rights voluntarily or involuntarily, both parents can sign a Temporary Power of Attorney for Our Minor Child, revocable at will, which allows him to live with you and allows you to enroll him in school, take him to the doctor, etc.