Need advise

I recently broke it off with my daughter’s dad not too long ago. It was an unhealthy relationship and we would argue more than we would actually get along. A few days ago we were arguing back and forth where things got out of hand and he almost put hands on me. I had to call the cops but he ended up leaving before for the cops got here. My daughter unfortunately saw it all. She has noticed that he has not been home since and asks me every night where her dad is. (She is 4). She cries to me and tells me she misses him and asks me when he will be coming home. How can I explain to my daughter that he won’t be coming home anymore? My heart hurts for her so bad. This is obviously for the better than her seeing what a toxic relationship her parents were in. But I just don’t know how to go about this bc she doesn’t understand what is going on. Please help.