#5 Seeking Solace
Kabuto came to Kakashi for solace—because he would never call it comfort.
It wasn't that he was ignored, or badly mistreated when he was with the Sannin. No, that wasn't it. While Orochimaru may be strict with him, and often harsh, he was never intentionally cruel unless the medic had somehow earned it—and he could do that, easily. So no, it wasn't "problems at home" that drove him to Konoha for his secret liaisons. At least, not completely.
Kabuto was starved. Starved for something other than bisque touches and brief physical trysts, which were often more rushed pleasure and stress relief than they were love-making. He was treated as what he was in the Oto: a tool. He was a valuable medic, had been a valuable spy, and he was exceptional at so many other things... It became him.
With Kakashi, Kabuto felt like a human. Despite his initial protest that he 'would not break', the Copynin handled him with such care that he felt... appriciated. Every curve of his body was sought out and caressed, heating him up slowly and letting him ride it out until the end. He was a man with Kakashi, and not a beautiful tool. In his strong arms, scarred hands, and warm bed, with no expectations and deadlines to speak of, Kabuto felt liberated. Even when the sex was rushed, the Jounin somehow found a way to make him feel worshiped. Perhaps it was all simply the man's style, to please his lover above all else. Whatever it was, Kabuto found his solace late at night, shuddering and groaning under the older man's hands.
He knew that it was wrong. It was wrong of him to sleep with the enemy without gain, and deceive his generous master and the kind-hearted Copynin. It was wrong of Kakashi, to betray his village by harboring a criminal those nights. If Orochimau ever discovered his affair...
As guilty as Kabuto felt, and he did feel a little guilty, he couldn't stop. A life of servitude didn't leave much room for being content, and he could only find it when he was used and adored all at the same time. And since neither Orochimaru or Kakashi could do it all by their selves, he sought solace in them both.