help.. the father of my child is doing drugs

I don't know what is the the best way to handle this. My daughter is 10
months old. I've noticed her father rapidly going out and "partying."
We live separately (which is best for now), but have been trying to
work on our relationship. Although, as long aas he continues to drink,
etc., I see us going nowhere. I don't know what to do anymore. I've
continuously expressed to him that he has a problem. He tells me he's
going to stop, but sure enough, the next weekend rolls around and he's
back alcohol and drugs. I don't know what to do. I have to think about
my daughter. I will not have her raised around this. Yet, I feel this
deep sadness & hope that he's going to stop. I feel like I just keep
waiting as it gets worse. I'm devastated at times & feel so lonely.
What is the best way for me to handle this, for everyone, especially,
my baby?
Has anyone gone through something like this? Or, does anyone has any
advice?
Thank you.