He may be telling himself he will get better. I know I told myself that for a long time. He will want to be away from other people doing drugs when he is really ready to stop doing them. I can understand your hurt for him letting this other person live with him. Just remember that while an addict is in active addiction they believe their own lies. They also are incapable of true feelings because they are constantly lying to themselves and to everyone else. It's almost like a bubble of lies they live in.. and it becomes more and more distorted the longer the addiction continues.
Congrats on making yourself better. No one deserves you healthy and great that you! Also, i'm sure it's a great example for your child. If he loses out on seeing his kid it's his problem. She will realize when she's older. I have a 7 year old and 3 year old with my RAH of iv heroin.