Wowee, a few things.
Have you gotten tested already? I imagine you have since you've been pregnant / had a baby already, but please make sure you and your baby girl are safe.
I'm sorry if this comes off as mean, but if your SO is a known cheater, why did you guys decide to have a baby together? You are obviously unhappy with her actions, and it was extremely unsafe for your baby's health to decide to have a baby with a known cheater and drug user, you never know what she could have been carrying.
Your SO is not going to be a parent and I think she made it obvious from the very start. If you want your baby to grow up in a healthy environment you need to take action now and get away from your SO. Since your SO has a bad history of cheating and drug use, and doesn't care to stop, I suggest taking some action not only for your health but for your baby girls. This is extremely unsafe. And you do not want to be with someone who constantly stays unfaithful and chooses drugs and video games over her family. Please be safe. I know it will be hard to take action, but I hope you can.