The more Kyouya thinks about it, the more he is intrigued by their relationship. He has tried before to figure it out, to reason and logically deduce all the reasons why they love one another and how their odd arrangement works for them, and he can never quite do it. It is like a mathematic equation that he can't answer, because he has no idea how to solve for three variables when the only constant is always changing.
He used to think of them in terms of grammar. Haruhi is The Subject, because the world encompassing the three of them usually revolves around her, and it is usually against her will. He is The Verb, because he doesn't like to waste words without having action of some sort. Following that same line of thought, he reckons that he is a Transitive Verb, as most everything it does has a direct effect the rest of the sentence, and it often makes or breaks its meaning. Tamaki is The Adjective, or The Interjection, or whatever other part of speech whose only significance laid deep within its triviality. Sentences could still survive without them, could still clinch business deals and give comfort during a thunderstorm and relay appreciation of beautifully-played piano music. They really were just useless jumblings of letters, but without them, the world would be painted only in black and white and a thousand indeterminate shades of grey.
And so he then begins to think of them in terms of art. Haruhi was undoubtedly White, with her pureness and her clear head and her ability to make sense of the chaos that continually surrounded her, but sometimes she is just a little bit Green too, especially in the courtroom. Kyouya was just as undoubtedly Black, a color that hinted at death and destruction and all things evil just as much as it subtly complemented White and everything it stood for. He thought that he was sometimes Purple as well, because Purple was a wealthy and sophisticated color that hated the early hours of the morning when Black seemed to take over everything it could get it hands on.
Tamaki is everything other color in the spectrum at one point or another during the course of the day, but mostly he is Orange. Orange seems to be a happy, cheerful color, and most of the time it is, even though Orange is the bastard child of Red and Yellow, and Brown won't ever let him forget it. Orange sometimes becomes a darker color, especially on the last day of October when it cons an unwilling Black into wreaking costumed havoc on the world. And Orange, like the child it is, enjoys every minute.
And sometimes Orange is Blue, but only when it is huddled in a corner thinking Black and White didn't love it anymore. Even though Orange knows full well that Black and White alone could only ever make Grey, a slightly mysterious being with Black's hair and eyes and White's blunt intelligence.
It is on the day that Ootori Kanaye is born that Kyouya begins to think of them in terms of mathematics. To most people, they are likely ((K∙H) + (T∙H) + (K∙T)). He knows that H and T do not think that way, and neither do ((H)(K)), HM, or MT. The people who know them the best perhaps think of them as (K∙T∙H) or (K∙H∙T), which are certainly not wrong ways to set up the equation. Most nights it starts out as (T∙K), because T is childish and impatient and insists that it is possible to wait for H to get out of the shower or to finish tucking in the baby, and it slowly morphs into (K∙T) + H, and from there into a warm, sticky mess of letters and multiplication signs that K is too aroused to care about graphing. The most correct way to write their particular equation is probably (K(T+H) + H(T+K) + T(H+K))=1, because on nights that are for whatever reason only (K∙H) or (K∙T), K feels as if K=⅔, and he knows that T and H feel the same.
But none of that is really right. It isn't right because Haruhi is not really a noun, Kyouya is not really a color, and Tamaki is not really an unknown, although Kyouya sometimes secretly thinks that he might be. Haruhi is Haruhi, just as Tamaki is Tamaki and Kyouya is himself. He will probably never be able to figure them out, because there is nothing that truly needs to be figured. They are nothing more or less than what they are—Tamaki, Haruhi, and Kyouya—and he should have learned by now not to question how anything involving Tamaki makes any sense whatsoever. Even if it is love.