In this case it's not Cullen's problems or personality but Dorian's. He has issues that he is not going to discuss with this man who he is only learning about. It's terribly difficult to let himself get close. He's not certain he's going to allow it when he plans on leaving.

"Oh, a gold piece? I'm willing to pay that if you turn out to be right." Dorian is tempted to argue about lyrium's effect on the human body and that Templars may eat more to counter act but he was only really learning the effects since coming here to the South. "I would buy you a drink but I imagine the tavern is still burned down."