Kabuto could never ditch oro because he loved oro too much and imo after kabuto was under sasoris control oro might have sensed something wrong with kabuto behaviour or characteristics which would have made him believe that he was under sasoris contro
I mean he would have ditched Oro before he had feelings for him.
Basically its like this:
Kabuto meets Oro and sees his awesome medical skills
Oro jumps out of sea to talk to Kabuto (end of last chapter)
Kabuto decides he doesn't want to join up with Oro
Kabuto meets Sasori and becomes his spy
Sasori makes Kabuto spy on Oro (puts the mind seal on him)
Oro breaks Sasori's control over Kabuto and convices him to work for him (this is where Kabuto and Oro start to date)
Sasori becomes Oro's double agent and spy's on Sasori and the rest of the Akatsuki
But we won't really know for sure until we see more of Kabuto's past.