If the police refuse to file an application for criminal complaint against the persons who assaulted you, you have the option of filing a private-party complaint in the district court that covers the town that the assault occurred in. It will cost you $15. Upon receiving the application and your affidavit of the facts alleged in support of the complaint, the clerk will schedule a clerk-magistrate's hearing and send a notice of the clerk's hearing to the other party(s). The other party(s) will have an opportunity to oppose the issuance of the criminal complaint at the clerk's hearing, either with or without their own attorneys. At the clerk's hearing, your witnesses or you would testify as to what happened, and the other party(s) could also testify. Note that if you testify, you may be incriminating yourself on your OUI or as to other crimes; you should speak to a lawyer to see if there are any self-incrimination issues before you testify.
You should also be focusing on defending your OUI charges. The facts you mention raise not only the possibility of a necessity defense, but of a lack of public way defense and a lack of operation defense. While not indicated in the facts you describe, perhaps the prosecution would also have a hard time proving the OUI either because you did not take a breathalyzer and/or did not complete any field sobriety tests and/or did not make any admissions as to how much you had to drink.
This is kind of a hard question to answer, without all the facts that are in the police report. Any steps the police don't take can always be used by your defense attorney at trial. These questions that you are posting really need to be directed to a defense attorney.
If you don't have an attorney you need to find one.
Clearly, you need a lawyer to assist you in this case. There is too much going on here to try and deal with it on your own.
This response does not create an attorney client relationship and is offered for informational purposes only. Only a lawyer fully versed on the facts and circumstances of your case can properly advise you on the case. I am licensed to practice in Minnesota, not every state. You should always consult with an attorney licensed in your area on how best to proceed.
You seem to be asking about the potential actions against your ex, and not about the defense of the case against you. Police have a degree of discretion as to the use of their resources. Do you have witnesses who will testify in support of your statement? If so, bring them to the police and ask agains that they investigate. You can also ask a clerk magistrate in the local district court to issue a complaint. Or you can file a civil case for your damages.
Whether any of this makes sense requires much more knowledge of the facts.
Evaluating any legal question requires a detailed knowledge of the specific facts involved. Since a short question will rarely contain all the relevant facts, the answer here should be considered a general comment for your consideration and not legal advice.
The police certainly do not have to follow-up upon your "statement." However, I think more interesting facts lie in the possible defenses of your OUI charge. As has been stated by previous, well-informed attorneys, it is imperative for a criminal defense attorney to review the police report.
I wish you luck.