How can I leave my girlfriend and get custody of our child?

I am currently still with my girlfriend. We have a daughter together. I am listed on the birth certificate as the father. My wife does drugs and she is mentally abusive to me and my daughter. I want to leave her but I want to make sure that I get custody of our daughter. Should I call CPS and tell them she is on drugs? Will they come out and drug test her immediately? If I take my daughter and leave the state without telling my girlfriend, am I breaking any laws?