When did you know the relationship was over with kids?

I just need to know when to know its over in a relationship with kids. My fiance and I have been fighting nonstop. Its a really long story but I don't trust him because of his addiction to pot and making me watch and take care of our 10 month old and my step daughter while he is high all the time and also when he drinks he is extremely violent. Never hit me but pretty close and just very verbally abusive. Anyways we have moved on from that but its not the same. He is trying but I feel like I have to walk on egg shells around him and my stepdaughter because he gets mad at me for telling her to pick up something that she drops and decides to leave it for me to pick it up. Mind you she is 11. Old enough to pick up after herself but I feel like emotionally I have checked out but everyone keeps telling me it will get better and being a single mom sucks and how I want more kids so I should stay and wait it out... I just don't know what to do anymore... i can't fathom the thought of my son being away from me and I do want more kids but I don't know if we are good for each other.