Drug Rehabilitation that works

How do I start… well I recently left my girlfriend that is 7 months pregnant, we were living together in east oakland with her mom from august 2009 to April 2010 over the course of those months I ended up getting her pregnant. Now the reason i left was because thinks weren’t going to well, she cheated on me, beat me a few times given me a black eye among other things, the verbal abuse was really bad and hateful I know i was stupid for staying but i just thought i loved her and didn’t want to abandon my kid, now i want to know if its possible to get full custody because I think she is unfit to be a mother and the house and area she lives in is horrible, her mother and older brother(parolee been in and out of group homes, still a meth addict) smoke weed everyday inside the house and its not a enviroment i want my child being exposed too. I just want whats best for him

thanks in advance