Hope's Peak Academy. Or in your words, absolute hell on Earth.
It was rumoured that a killing game took place in that school, which is why the school was shut down in the first place. Some people believed it happened, and some people believed it was just a made up story to explain why the school was shut down. Kurapika never really believed in silly rumours like that, but he couldn't help but wonder... if that killing game did happen, what caused it to happen? Mass psychosis, or something else?
Curiosity eventually got the better of him, and he researched everything he could on it, eventually reaching files with the names of the students who were involved in the incident. He froze when he saw one name. Yours. He frowned slightly, realising that you were there during the Hope's Peak Academy murder game incident. Of course, it could all just have been put there by someone to make others believe that it happened, but... it had a little more information. Information that was true. Why didn't you tell him this? He told you about his past, yet you never mentioned anything about this. Did you... not trust him enough? You were his lover, and yet... you hid this from him.