The angel didn't know what his body was doing, couldn't begin to understand why it (and by extension, he) wouldn't listen to him. He flinched away from that tongue and the suggestion that might've been true on some level. It was something Samandriel didn't want to think about. He was still learning how things like desire worked.
"I think you're going to do what you like no matter what I say," he said, realizing only after he'd flinched away that such movement only exposed more of his neck to the vampire.
His former life was his own shame to bear, and he wouldn't have that associated with Mitchell at all. "Are you to be my punishment then? Sent from on high because I dared to keep on living?" Or perhaps sent by Zachariah. In a sense, they were still one in the same.