there might not be any evidence that Kabuto, like Kimimaro and Haku, is in love with his evil boss. Hell, even Kimimaro never said that he loved Orochimaru (but I still think you're blind and dumb and/or homophobic if you can't at least understand why some people say that Kimi's affection for Oro was tinged with love).

But I do think Kabuto is extremely loyal to Orochimaru. He saved his life when Tsunade feigned healing him. He helps with tons of body transfers. He works almost like Orochimaru's personal doctor at times. I mean, Kabuto didn't even blink when Oro's plan to destroy Konoha failed and Oro was left crippled, let alone act like he wanted to abandon him.

There was that episode where Kabuto went to kill Sasuke. But he didn't. And, when you ask yourself WHY Kabuto would have gone and killed Sasuke, what reasons can you come up with? That he wanted to thwart Orochimaru's plan? No, he would have screwed him over at some other crucial point.

The only reason I could ever think of for why Kabuto wanted to kill Sasuke is that he was afraid Sasuke would replace him as Oro's right hand man. He couldn't stand how obsessed Orochimaru was with Sasuke. And, if you care to examine that line of thought further, it's not hard to take Kabuto's paranoid-jealousy of Sasuke to an extension of his feelings toward Orochimaru.

But, this all being said, I can't see why the spy couldn't be Kabuto. Remember, Yuura was absolutely loyal to the Sand, without even the faintest ideas of treachery, but Sasori's jutsu took control of him anyway. It's not like Sasori's spy is something people choose to be...