This is what often happens:
The "victim" makes a report (or someone does so on his/her behalf).
Too often, the "victim" recants, and wishes to have charges dropped. The SA/DA knows this, and as many as 70% of DV victims try to make it all go away.
Thankfully, the State almost expects the victim to recant - thus their testimony is not always needed in order to convict the alleged offender.
Practical advice: Never, ever call the police in order to get your partner to calm down - that is NOT what's going to happen. Once you call the police, the whole thing is basically out of your hands.