Disclaimer: Again, not mine. Get used to it.
Someone once asked Kabuto for advice on being a double agent. He responded that he isn't a double agent.
And it's true. Kabuto's game is much more complicated, much more subtle than that. He's a quadruple agent. And all his sides believe, or have believed, that he was playing strictly for them.
Konoha believed that up until Kabuto was standing in the Chunnin Exams arena, facing off against Kakashi. Kakashi himself had know since he stumbled in upon Kabuto with a knife to Sasuke's throat. The jutsus he used were somewhat of a giveaway, honestly. Most Konohans weren't that surprised.
Akatsuki believed that up until Kabuto beheaded a fake Sasori, believing it was real. That was a rude awakening.
Orochimaru has had doubts, but he still believes it. Kabuto has never given him reason not to. It'll probably be fatal for him to realize it. He may die before he does. He may die after he does. Kabuto's pretty sure he'll never figure it out. Who's going to tell him?
Kabuto is ultimately loyal to himself. He knows most people consider this narcissism. He thinks it's just being honest. Who else deserves his loyalty? One day, though, Kabuto's going to encounter the cross roads all spies encounter; he's going to have to make a choice. For most intelligence shinobi, that choice is hard. For most double agents, it forces them to reevaluate everything they think they know.
If Kabuto's not careful, it's going to pull him asunder.
If he is, it's going to tear him (metaphorically) apart.
He's not worried about it.