That's a shitty excuse. A monarch is inherently a populist figure, kings and emperors have always been populist in nature and ergo at odds with the merchants and aristocrats that are beholden to them. An inherent aspect of the nature of such a ruler is that what they can do is limited by what they can get away with in the public eye, and by not much else. If he had wanted to, he could have exposed the plot to the public, executed those responsible, and simply absorbed the backlash it would cause. He would have endured the hit, because even if it caused diplomatic and political problems, the vast majority of the people would have wholeheartedly supported his actions. Instead, he not only allowed the perpetrators to get away with it, he married the person responsible. His wife died, and his son could very well have been in a coma for the rest of his life.
A good king and a good country are symbiotic. The king defends the people, and the people defend the king. A king represents the nation, as a symbol, so if something happens to the king and it's allowed to stand, then it reflects poorly on every single person in that nation, because they've allowed the slight to stand. A slight to the honor of the king is a slight to the honor of all. People have gladly followed kings and emperors not just into hard times, but into outright war because of murdered family or jilted love. If this is the king's idea of love, then no one should want anything to do with it. He is an unworthy king who has no faith in his subjects, and even less faith in himself.