He never promised fidelity
Here you go Nick, straight from your Lord and God, in the Sermon on the Mount. Jesus was more concerned about your intentions than stupid semantic games.
“You have heard that it was said, ‘You shall not commit adultery.’ But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. If your right eye causes you to stumble, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell. And if your right hand causes you to stumble, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into hell.
“It has been said, ‘Anyone who divorces his wife must give her a certificate of divorce.’ But I tell you that anyone who divorces his wife, except for sexual immorality, makes her the victim of adultery, and anyone who marries a divorced woman commits adultery.
Now, I wasn't a guest at the Rackets' wedding, but unless the Scandanavian Incel Prudes are doing marriage in some real weird type of way, I'm going to bet that the ceremony involved oaths of fidelity to each other before the respective families and God. Vows that I'm almost certain that Nick has dishonored, thoroughly.
"Whom, then, was he trying to deceive when he made it? God? That was really very unwise. Himself? That was not very much wiser. The bride, or bridegroom, or the in-laws? That was treacherous. Most often, I think, the couple (or one of them) hoped to deceive the public. They wanted the respectability that is attached to marriage without intending to pay the price. If people do not believe in permanent marriage, it is perhaps better that they should live together unmarried than that they should make vows they do not mean to keep. It is true that by living together without marriage they will be guilty (in Christian eyes) of fornication. But one fault is not mended by adding another; unchastity is not improved by adding perjury".
— C.S. Lewis