“Is it inauthentic or dishonest for two Christians to remain married when they don’t get along?”
It is simply a sad fact of life that not every Christian enjoys the company of every other Christian at every moment. Almost everyone grinds our gears in one way or another. As soon as the honeymoon is over (and sometimes before), you will find out things about your partner you didn’t know and don’t like. Put two very different believers under the same roof, bind them legally and spiritually to one another, and you have a recipe for persistent unhappiness when one or both behave unbiblically.