That's the nature of abusive relationships, my love.
At this point, I'd be inclined to arrange an interview with your social worker and ask her if she can bring her supervisor as well. Find out exactly what is going on, and where they're intending to go to here. Also, without going into details, I would tell them that there is a relationship breakdown right now.
I need you to know that when I hit the point where I decided to wean cold turkey, I was hospitalised three days later. It sounds like your ex has forced you to keep going a little bit longer- not a good thing, admittedly, but still. You simply do not have the luxury of living under this much stress for much longer, because sooner or later you need to break under the pressure. There is a possibility that the social workers can help you get the help that you need, that isn't going to involve separating you from your baby. This is why I'm suggesting, so strongly, that you talk to them and ask for help.
I'd also get a family lawyer lined up- it sounds like SleeplessMommy has some good help for you there- and I'd get CPS and the lawyer talking to each other as well. It sounds like you have four goals: to keep parental rights and custody, to get that man out of your hair, to get well again and to finish school and be the lawyer and parent you dreamed of being. All of this is possible, but you need to believe in yourself and you need to accept help where it's offered.
Life on the other side of PPD can be awesome, btw. I know you're in the depths of it now, but seriously, there is life after depression.