The elements of a malicious prosecution action in Washington State are that the defendant instituted or continued the prosecution, that the defendant did so without probable cause and with malice, that the proceeding terminated on the merits in favor of the plaintiff or was abandoned, and that the plaintiff suffered injury as a result of the prosecution.
The dismissal of criminal charges establishes a prima facie case of lack of probable cause. However, if the defendant officer gives a full and fair disclosure of all material facts known by the officer to the prosecutor, in good faith, and then the prosecuting attorney decides to file charges, the defendant has established probable cause as a matter of law.
You have not indicated in your post that the prosecutor committed acts that could be interpreted as malicious prosecution. Perhaps there are some additional details that you omitted?
If you do not believe that you can prove damages, be aware that you cannot prevail in a malicious prosecution action without proof of a compensable injury. That's an element of a valid cause of action. It may be possible to show damages through proof of arrest, seizure of property, or interference with your person because of the malicious prosecution.
Be aware that if your ex- showed evidence of an injury, your protestation that you inflicted the injury in self-defense is not sufficient to create a malicious prosecution case if you're arrested for inflicting those injuries, even if a prosecutor later decides that you were telling the truth or the case cannot be proved due to competing narratives.

