Had an old supervisor, Noel, who was an ex-cop. His policy on domestic disturbances was to haul both parties in. His reason for this: once he got there it was nothing more than a he said she said. By taking in both at the same time, he said, it was amazing how many times the truth actually came out. In your case the truth was out before you were taken in, but he hated the idea that it was always the man's fault and therefore the man should get arrested. He said in his experience once both were in cuffs it usually turned out to be a 50/50 split. We need more cops who think like that.