Child Custody?!

I been together with my boyfriend and he has another child with another girl. He has been upset he has even cried because his baby mother doesn't want to let him see his daughter. She is a drug addict and acholic and she is known to have suicidal thought. My boyfriend has asked me many question about if he could get custody of his daughter and I don't really know what to tell him I support him all the way on whatever he wants to do!