OK, my best guess for whats happening, let jump right into it. So the doctor has a clone Sid killed the clone thinking it was the doctor. He did this because the doctor potentially could save our demon seme daddy.
So the conversation now is the doctor not wanting to die and weighing his options. Sid just now told Seme demon daddy that the doctor is dead. He did this to cover up the fact that he didn't bring the doctor to daddy demon.
Now, Cain has no reason to trust the doctor but he clearly has trust for Sid. Yes, Cain indeed has threatened Sid but to me that came across as Cain covering his bases and not really believing he's been betrayed.
So the doctor is smart and knows something wrong is going on. I'm pretty sure he's figured out that Cain didn't order his attack but he's also sure that Sid would kill him and convince Cain it was for the best. So right now he covered Sids stupid till he can build repore with Cain and then expose Sid.
Also side note the ugly guy that got shot has the artifact not Sid. If Cain calls for it and the other demon shows up it would basically prove Sid is a butt head.
O,k I feel crazy but I remember a couple more chapters after vol 2. Did I have hallucinations?