Wow, you are such a good person to be doing this, especially since you'd not even sure he's the dad. I wish you the best in all this, and I really, really hope that the boy ends up in the right hands (yours, obviously).
If it makes you feel any better, my cousin had a very similar situation her now daughter. One of our other relatives had a baby girl and the mother was addicted to alcohol and possibly (probably) drugs. They would leave the baby in her diapers for hours if not days. There was garbage all over their house, covering everything. They never cleaned. Finally, my cousin and aunt were supposed to babysit her and they just did not let her go back. They filed to have the baby taken away (nearly 2 years at this point), and my cousin kept her with her son and daughter who were about 5 and 13 years old at the time. At first the mother seemed to be fine with it and then after a few months decided she wanted to have her back. For a while she was going to rehab and all that, but we all knew she was just going to go back to her old ways. Finally, they proved she was unfit, and my cousin has adopted her. She is the cutest little girl and is now about 4. And not surprisingly, the mother is a drunk once again same as her dad.
So, don't give up hope! It might take some time, but with legal help, you will probably get him.