If I was Sasuke, I'd be making plans to kill Orochimaru right now. It has nothing to do with the whole "best friends" thing; I highly doubt that Sasuke and Oro are friends (gay jokes aside), but there are a few good reasons to kill Oro now.
First, Orochimaru's current body is wearing out; he'll need to take his next host soon. I don't think anyone here believes that Sasuke will end up being Orochimaru's host.
Second, Orochimaru would be a strong opponent. By this time Sasuke has probbably beaten everyone in sound village a dozen times over, and he needs to fight the most powerful opponent.
Third, Orochimaru just beat Naruto. Sasuke will probably hear about this -- if not from Oro then from Kabuto, Sai, or someone else. If Sasuke can kill Orochimaru when Naruto could not, then that proves who is stronger.
Given this, Sasuke's next logical move would be to kill Orochimaru.