My estranged husband has physically assaulted me 3 times in the past 2 years, most recent on 03/29, which I reported to MPD. I was left with visible injury. But ge was never arrested. How is that he is above the law and can attack

You should escalate the situation. Talk to officers superiors.

Get an emergency restraining order that takes effect immediately and if he violates it he will automatically go to jail and a warrant for his arrest will be filed so that if he is stopped for any reason, anywhere in the state he will immediately be cuffed, arrested and taken to jail. Keep journal with you at all times and make detailed notes of all interaction with him- take photos of any damage he caused to property or yourself for evidence