You likely should review your facts and options with an attorney.
There is no legal prohibition that would prevent you from divorcing your spouse simply because he is in prison. Whether you should divorce is something that you should discuss with your attorney. (In WA, divorce is called a dissolution of marriage.)
the fact that he is in prison is not legally relevant. serve him in prison with the divorce papers and get divorced. given that he is in prison, he may be willing to sign the joinder and you would have an uncontested divorce. if not, he would have to get an atty to represent him at trial, eventhough he personally couldn't attend the trial.
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