I agree that it is probably not a good idea to talk to police about the incident without at least having an attorney present. However, the fact that you have not been charged yet is a good sign. My experience is that the DA'S office will usually charge domestic violence cases very quickly. The fact that you were never arrested probably means that no charges will be filed.
You may have made a big mistake by going and talking to the police - they are not looking to do anything other than get the information they need to arrest you, and you should never talk to the police without first consulting with a lawyer.
The government may file charges against you many months from now.
Unfortunately, you can't know for sure that a DA won't charge you with something until and unless the statute(s) of limitations (SOL) have passed. The section of the Oregon Revised Statutes that holds the answer to how long a DA has to file charges is 131.125. However, in order to make use of 131.125, you would need to know what charges you are potentially facing. There is no way to tell for sure what crimes the DA might allege, but most likely you would be looking in ORS 163 and specifically 163.160 et seq. It sounds as if the highest the DA would go would probably be Assault IV, a Class A misdemeanor. That has a SOL of two years. However, if the DA buys your ex's version of events, you could potentially be looking at a Class C felony under ORS 163.165 or 163.213. Then the SOL would be three years.
All that being said, unless the DA is bringing the case before the grand jury (seeking felony charges), it sounds as if they are not pursuing it. The short answer to your question is, technically, you probably have 2-3 years to wait. Practically, however, if they haven't filed anything within 30-60 days, you're probably all right.
Although not part of your question, it is generally a good idea NOT to talk to a law enforcement officer, particularly if you are the suspect in an alleged crime and particularly without legal representation.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.