If you maintain a residence in Idaho, while you are working and living in Washington state, combined with the additional fact that your spouse lives in Idaho, almost certainly makes you an Idaho resident for state income tax purposes. That said, however, you can review the following Idaho legal materials, and make that determination for yourself (or see if you qualify for a narrow exception to Idaho residency for tax purposes).
Please see this Idaho State Tax Commission webpage:
https://tax.idaho.gov/i-1039.cfm
Also, look to Rule 030, as shown on Page 14, of the Idaho State Tax Commission administrative guidelines found here:
https://adminrules.idaho.gov/rules/current/35/0101.pdf
Finally, please read the Idaho state residency law itself, which is codified as Idaho Statutes Title 63, Chapter 30, Section 13, as found here:
https://legislature.idaho.gov/statutesrules/idstat/title63/t63ch30/sect63-3013/Those materials will provide you a 100% definitive answer to your Idaho residency question, which ultimately determines if you need to file an Idaho tax return (and pay taxes to Idaho on your income earned in Washington state).
Thank you for asking this important question.
