After the death of Knox, Roman spent a little time debating whether or not he could trust his Uncle Castor.
On Star-Crossed Season 1 Episode 9, it became clear that his initial instincts were spot on: Castor is not a good guy.
Admittedly, we've all known that there must have been something else going on behind Castor's well intended exterior. He was almost trying a little too hard.
Castor also always had secretive plans or shady side dealings. He wanted Roman and Emery apart for another reason than the Trags. He had a hidden stash of bombs that would help get rid of Black Cyper. Then there's always the reminder that Castor was once a Trag himself.