Reine was lost, his mind was in chaos, everything that Leviath said to him was hard for him to accept, thought he was taken advantage by many in the past, He didn't espect that Leviath would do something like this.
Sor right from the start, Leviath knew about who he was, and though Reine never told him about who he was or that he was looking for his people, he should've atleast known that Reine was searching for his origin, and if he truly knew about who he was, then he had every right to know who he was, and what he was, and exactly what he meant when he said to him that he came to ruin his mission, because right from the start, Reine knew nothing about all of this, let alone the mission this mad man was talking about, but he had to know, he had every reason to know, this was about him after all, so he had to know, and that too right now.